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Composition of air - class-VII

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Dinitrogen and dioxygen are main constituents of air, but these do not react with each other to form oxides of nitrogen because:

  1. the reaction is endothermic and requires very high temperature

  2. the reaction can be initiated only in presence of a catalyst

  3. oxides of nitrogen are unstable

  4. $N _{2}$ and $O _{2}$ are unreactive


Correct Option: A
Explanation:

The main component of air are oxygen and they will only react together at a normal temperature. For the formation of oxides of nitrogen, a very high temperature is required. 

Clothes dry faster in summer than in monsoon days. Why?  

  1. Because dry air is less humid

  2. Wet air is less humid

  3. Dry air is more humid

  4. None of these


Correct Option: A
Explanation:

In monsoon there is lot of humidity in air as compared to summer. Hence, the Clothes dry faster in summer than in monsoon

Warm air is heavier than cold air. State whether the above statement is true or false and explain.

  1. True, because warm air contains more heat

  2. True, because warm air molecules are separated by greater distances

  3. False, because molecules of warm air expand and become less dense

  4. False, because cold air contain extra temperature than hot air


Correct Option: C
Explanation:

Warm air is lighter than cold air because they have more heat energy, which results in the increase in distances between the molecules. This decraeses the density, and hence makes it lighter than cold air.

During night time which is more prevalent?

  1. Sea breeze

  2. Land breeze

  3. Both A & B

  4. None of these


Correct Option: B
Explanation:

Land breeze is defined as a coastal breeze blowing at night from land to sea, caused by the difference in the rate of cooling of their respective surfaces.
Sea breeze is defined as a breeze blowing towards the land from the sea, especially during the day owing to the relative warmth of the land.

Sea and land breezes are caused because of:

  1. Convection

  2. Cyclones

  3. Rains

  4. Conduction


Correct Option: A
Explanation:

Sea and land breezes are caused because of an uneven heating of the earth and through convection currents.

So, the answer is Convection

Water droplets on grass and rocks is called:

  1. Dew

  2. Snow

  3. Rain

  4. Smog


Correct Option: A
Explanation:

Dew are tiny drops of water that form on cool surfaces at night, when atmospheric vapour condenses.

Nitrogen is the major constituent of air.

  1. True

  2. False


Correct Option: A
Explanation:

Nitrogen is the major constituent of air. 

It constituents about $78\%$ of total volume of air. 

Argon is the major constituent of inert gases present in air.

  1. True

  2. False


Correct Option: A
Explanation:

Argon is the most abundant and most used of the noble gases. Its chief uses are in metallurgy, where it provides an inert atmosphere in which hot metals can be worked. Because argon is so very unreactive, it prevents chemical reactions of the very hot metal being welded or forged.

Nitrogen constitutes nearly __ % of the atmosphere.

  1. 45

  2. 78

  3. 21

  4. 0.03


Correct Option: B
Explanation:

Nitrogen constitutes nearly 78% of the atmosphere.

Statement: Nitrogen is slightly heavier than air.


State whether the given statement is true or false.

  1. True

  2. False


Correct Option: B

Which of the following is correct about the percentage composition of $O _2$ in air?

  1. 21%

  2. 52%

  3. 78%

  4. 12.5%


Correct Option: A
Explanation:

The air in our atmosphere is composed of molecules of different gases. The most common gases are nitrogen (78%), oxygen (about 21%), and argon (almost 1%).

__________ and __________ are the major components of the atmosphere.

  1. Nitrogen and argon

  2. Carbon dioxide and oxygen

  3. Nitrogen and oxygen

  4. Oxygen and carbon dioxide


Correct Option: C
Explanation:

Nitrogen and oxygen gases are the major components of the atmosphere. Around 80% of the atmosphere is nitrogen and 20% is oxygen, by volume. 

The gases which are inert and present in extremely low concentrations are:

  1. neon

  2. helium

  3. argon

  4. xenon


Correct Option: D

Air consists of active and inactive components. This was proposed by _______________.

  1. Mayow in the year 1674

  2. Maeow in the year 1764

  3. Miaw in the year 1864

  4. None of the above


Correct Option: A
Explanation:

Air consists of active and inactive components. This was proposed by Mayow in the year 1674.

Noble gases have the _________ among the elements of each period.

  1. Largest ionization potential

  2. Lowest ionization potential

  3. Greatest melting point

  4. Low electronic configuration


Correct Option: A
Explanation:

Noble gases have the largest ionization potential among the elements of each period, which reflects the stability of their electron configuration and is related to their relative lack of chemical reactivity.

Noble gases have low boiling point because:

  1. Weak intermolecular force

  2. Strong intermolecular force

  3. Cannot withstand heat

  4. Both a and c


Correct Option: A
Explanation:

The noble gases have weak interatomic force, and consequently have very low melting and boiling points. They are all monatomic gases under standard conditions, including the elements with larger atomic masses than many normally solid elements.

Noble gases are members of ______ periodic table.

  1. Group 1

  2. Group 18

  3. Group 17

  4. Group 6


Correct Option: B
Explanation:

The noble gases make a group of chemical elements with similar properties. For the first six periods of the periodic table, the noble gases are exactly the members of group 18 of the periodic table.

Which of the following is most abundant on earth except from hydrogen?

  1. Krypton

  2. Helium

  3. Neon

  4. Argon


Correct Option: B
Explanation:

The abundances of the noble gases decrease as their atomic numbers increase. Helium is the most plentiful element in the universe except hydrogen. All the noble gases are present in Earths atmosphere and, except for helium and radon, their major commercial source is the air, from which they are obtained by liquefaction and fractional distillation.

An inert gas is a gas that is:

  1. Highly reactive

  2. Non-reactive

  3. Both a and b

  4. None of above


Correct Option: B
Explanation:

An inert gas is a gas that is generally non-reactive with other substances. The term inert means non-reactive. We refer to gases as being chemically inert if their atoms don't combine with other atoms in chemical reactions.

All the noble gases have $8$ electrons in their outermost shell except :

  1. $Ar$

  2. $Kr$

  3. $Ne$

  4. $He$


Correct Option: D
Explanation:

All the noble gases have 8 electrons in their outermost shell except  Helium (He) which has only 2 electrons in its outermost shell.

Most common inert gases are:

  1. Helium

  2. Krypton

  3. Argon

  4. All of above


Correct Option: D
Explanation:

When we refer to inert gases, we are usually referring to six primary ones, also called the noble gases. Meet the most common inert gases: helium $\left(He\right)$, argon $\left(Ar\right)$, neon $\left(Ne\right)$, krypton $\left(Kr\right)$, xenon $\left(Xe\right)$, and radon $\left(Rn\right)$.

The amount of water vapour in air is termed as:

  1. humidity.

  2. dew.

  3. mist.

  4. none of the above.


Correct Option: A
Explanation:

Humidity is the amount of water vapour in the atmosphere. It is a significant aspect of atmosphere beacuse it effects the weather and climate.

Why are some gases inert?

  1. They are stable

  2. They have 5 electrons in their last shell

  3. They do not have sufficient atoms to react

  4. All of above


Correct Option: A
Explanation:

Most atoms do not have 8 electrons in this outer orbital so they react with other atoms to form bonds to fill their outer electron orbital. The atomic structure of the noble gases is different from the structure of most atoms because they have a filled outer orbital.

Which of the following is used in balloons and airships?

  1. Argon

  2. Neon

  3. Helium

  4. Carbon


Correct Option: C
Explanation:

Helium is used in balloons and airships. It is much less dense than air, so balloons filled with it float upwards.

Nitrogen is liberated by the thermal decomposition of only :

  1. $NH _4NO _2$

  2. $NaN _3$

  3. $(NH _4) _2Cr _2O _7$

  4. All of these


Correct Option: A
Explanation:

$ { { (NH } _{ 2 }) } _{ 2 }{ Cr } _{ 2 }{ O } _{ 7 }\xrightarrow [ thermal\quad decomposition ]{ \Delta  } { Cr } _{ 2 }{ O } _{ 3 }+{ N } _{ 2 }+4{ H } _{ 2 }O\ N{ H } _{ 4 }{ NO } _{ 2 }\xrightarrow [ thermal\quad decomposition ]{ \Delta  } { N } _{ 2 }+2{ H } _{ 2 }O\ 2{ NaN } _{ 3 }\xrightarrow [ thermal\quad decomposition ]{ \Delta  } 2Na+3{ N } _{ 2 } $ 


Hence, all of these. 

Main constituent in air is:

  1. nitrogen

  2. oxygen

  3. argon

  4. water vapor


Correct Option: A
Explanation:

Main constituent in air is nitrogen.
The proportion of nitrogen in the open air is 78% by volume.
Note:
Air is a mixture of gases. The volume percent of nitrogen and oxygen are 78%and 21% respectively. Air also contains tiny amounts of carbon dioxide, argon, methane, ozone and water vapour.

Which of the following noble gas is used in light bulbs?

  1. Helium

  2. Neon

  3. Krypton

  4. Argon


Correct Option: D
Explanation:

Argon is used in light bulbs. The very thin metal filament inside the bulb would react with oxygen and burn away if the bulb were filled with air instead of argon. Argon stops the filament burning away because it is unreactive.

Combustion can not take place without:

  1. water

  2. carbon

  3. air

  4. zinc


Correct Option: C
Explanation:

Combustion can not take place without air. Air contains about 21% by volume of oxygen. Oxygen is essential for combustion to occur.

Which of the following compounds produce $N _2$ on strong heating?

  1. $NaNO _2$

  2. $NaNO _3$

  3. $NH _4NO _2$

  4. $AgNO _3$


Correct Option: A
Explanation:

The thermal decomposition of sodium nitrite to produce sodium oxide(III), nitrogen and oxygen. This reaction takes place at a temperature of $700-900°C.$

$4NaN{ O } _{ 2 }→2{ Na } _{ 2 }O+2{ N } _{ 2 }+3{ O } _{ 2 }$

Which of the following substances is most useful in removing nitrogen from air?

  1. Phosphorus

  2. Lime water

  3. Calcium carbide

  4. Magnesium


Correct Option: B
Explanation:

A mixture of nitrogen and carbon dioxide can be distinguished by passing it through lime water. Because nitrogen does not turn lime water milky and carbon dioxide forms carbonate with lime which makes lime water milky. From this we can conclude that nitrogen gas does not react with lime water, hence, it is most useful in removing nitrogen from air.

Pure nitrogen can be prepared from :

  1. $NH _4OH$

  2. $Ca _3N _2$

  3. $NH _4NO _2$

  4. $Ba(NO _3) _2$


Correct Option: C
Explanation:

$ N{ H } _{ 4 }{ NO } _{ 2 }\xrightarrow [ thermal\quad decomposition ]{ \Delta  } { N } _{ 2 }+2{ H } _{ 2 }O $

Pure nitrogen can be prepared from $ N{ H } _{ 4 }{ NO } _{ 2 } $.

Oxidation of ammonia yields :

  1. $NO _2$

  2. $N _2O$

  3. $N _2O _3$

  4. $NO$


Correct Option: D
Explanation:

 The exothermic oxidation of ammonia to nitrogen oxide and water vapour:

 $4N{ H } _{ 3 }+5{ O } _{ 2 }→4NO+6{ H } _{ 2 }O$

The group of elements which is the most inert is:

  1. halogens

  2. actinides

  3. noble gases

  4. group 1A alkali metals


Correct Option: C
Explanation:
Noble gases have their octet fulfilled, that is their outermost shell is completely occupied. Hence, noble gases are very inert in nature with little scope of reactions.

The third most abundant gas in Earth's atmosphere is:

  1. carbon

  2. nitrogen

  3. oxygen

  4. argon


Correct Option: D
Explanation:

The atmosphere contains many gases, including some pollutants and greenhouse gases. The most abundant gas in the atmosphere is nitrogensecond oxygen . Argon, an inert gas, is the third most abundant gas in the atmosphere.

Which of the following statements is/ are true about nitrogen?

  1. It has small size.

  2. It is very difficult to identify.

  3. It is a typical non metal.

  4. Ease of formation of triple bond.


Correct Option: A,B,C,D
Explanation:

Nitrogen has small size and it is a typical non-metal. It is very difficult to identify. It can easily form a triple bond.

Inert gases are also known as___________.

  1. zero-valent gases

  2. zero group elements

  3. noble gases

  4. All of the above


Correct Option: D
Explanation:

Inert gases are also known as zero-valent gases, zero group elements or noble gases. They have completely filled valence shell and are chemically unreactive.

At low temperatures, nitrogen:

  1. is poisonous

  2. is highly soluble in water

  3. can be liquefied on compression

  4. dissociates to form nascent nitrogen


Correct Option: C
Explanation:

At low temperatures nitrogen can be liquefied on compression.

Oxygen is returned to the atmosphere mainly by :

  1. burning of fossil fuels

  2. respiration

  3. photosynthesis

  4. fungi


Correct Option: C
Explanation:

Oxygen is returned to the atmosphere mainly by photosynthesis.


Hence the option C is correct.

Choose the correct statement from the following:

  1. Nitrogen is neutral to litmus.

  2. Nitrogen is a non-combustible and non-supporter of combustion.

  3. Nitrogen is a poisonous gas.

  4. At low temperature, nitrogen can be liquefied on compression.


Correct Option: A,B,D
Explanation:

Nitrogen gas is neutral to litmus and is a non combustible nor supports combustion and can be liquefied on compression at low temperatures. It is non poisonous.

Nitrogen is not a supporter of:

  1. Combustion

  2. Decomposition

  3. Both A and B

  4. none of these


Correct Option: A
Explanation:

Nitrogen is not a supporter of COMBUSTION.
Nitrogen is a colorless, odorless, tasteless diatomic gas. It is found in Group 15 of the periodic table. It does not burn, does not support combustion, and is only slightly soluble in water. It is relatively inactive chemically, but many of its compounds display marked reactivity.

In solid state, nitrogen occurs as:

  1. Chile saltpeter

  2. Saltpeter

  3. Sal ammoniac

  4. All of these


Correct Option: D
Explanation:

 In solid state, nitrogen occurs as chile saltpeter, saltpeter and sal ammoniac.
Chile saltpeter is sodium nitrate, $\displaystyle NaNO _3$.
Saltpeter is potassium nitrate, $\displaystyle KNO _3$
Sal ammoniac is ammonium chloride, $\displaystyle NH _4Cl$.

In combustion nitrogen work as:

  1. non supporter

  2. supporter

  3. highly supporter

  4. light supporter


Correct Option: A
Explanation:

Nitrogen is a non supporter of combustion.
Nitrogen is a colorless, odorless, tasteless diatomic gas. It is found in Group 15 of the periodic table. It does not burn, does not support combustion.

Air has________ composition with________ oxygen at high attitudes.

  1. fixed, less

  2. variable, less

  3. variable, more

  4. fixed, more


Correct Option: A
Explanation:

Air has fixed composition with less oxygen at high altitudes. Air contains 78% nitrogen and 21% oxygen and less than 1% He, Ar, Ne and water vapor content. This composition remains fixed at all locations but the oxygen becomes less dense at high altitudes so it is difficult to breathe in such low concentration of air.

During day time which of the following is most prevalent?

  1. Sea breeze

  2. Land breeze

  3. Both A & B

  4. None of these


Correct Option: A
Explanation:

Sea breeze is defined as a breeze blowing towards the land from the sea, especially during the day owing to the relative warmth of the land.

Rearing of silk worm is known as:

  1. Silviculture

  2. Sericulture

  3. Apiculture

  4. Horticulture


Correct Option: B
Explanation:

Silviculture is growing and cultivation of trees.

Sericulture is production of silk and rearing of silkworms.
Apiculture is also called beekeeping.
Horticulture is the practice of garden cultivation and management.
Hence, option B is correct.

Which of the following statements is true regarding earth's atmosphere?

  1. It gets denser with increase in altitude

  2. It gets thinner with increase in altitude

  3. Its thickness is atleast one-fourth the radius of the earth.

  4. It contains no solid particles


Correct Option: B
Explanation:

The earth's atmosphere gets thinner with the increase in altitude. The earth's atmospheric layers are Troposphere, Stratosphere, Mesosphere, Ionosphere, and Exosphere. Each layer has its own importance. 

Option (B) is correct.

Mountaineers carry oxygen cylinders with them because :

  1. oxygen supports combustion

  2. air becomes thinner as we go higher

  3. air is denser as we go  higher

  4. none of these


Correct Option: B
Explanation:

Mountaineers carry oxygen cylinder along with them because when they climb mountains, as altitude increase, the amount of oxygen level in the atmospheric air decreases as trees are not found at higher altitude.


As a result, mountaineers suffer from dizziness. It can also lead to hypoxia.


Hence, te correct option is $\text{B}$

It is not proper to breathe through our mouth because:

  1. the dust particles would enter our bodies

  2. more carbon dioxide will be inhaled

  3. our throat will become sore

  4. we will catch cold easily


Correct Option: A
Explanation:

It is not proper to breathe through our mouth because most of the dust particles can enter our body along with the air we breathe in. But breathing through nose does have this because nose has hair present which traps the dust particles.

The correct ascending order of gases as per their composition in air is:

  1. oxygen< carbon dioxide

  2. hydrogen < oxygen < nitrogen

  3. nitrogen < hydrogen < oxygen

  4. nitrogen < oxygen


Correct Option: B
Explanation:

By volume dry air contains $78.09\%$ Nitrogen, $20.95\%$ Oxygen, $0.93\%$ Argon, $0.04\%$ Carbon dioxide and small traces of other gases.


Ascending order of gases as per their composition in air is-

Hydrogen $<$ Oxygen $<$ Nitrogen

The proportion of nitrogen in the open air is:

  1. $21$% by volume

  2. $50$% by weight

  3. $21$% by weight

  4. $78$% by volume

  5. $29$% by volume


Correct Option: D
Explanation:

The proportion of nitrogen in the open air is 78% by volume.
Note:
Air is a mixture of gases. The volume percent of nitrogen and oxygen are 78%and 21% respectively. Air also contains tiny amounts of carbon dioxide, argon, methane, ozone and water vapour.

Which of the following gases do not form part of the atmosphere?

  1. Nitrogen

  2. Chlorine

  3. Carbon idoxide

  4. Oxygen

  5. Ozone


Correct Option: B
Explanation:

Nitrogen$(N _2)$, Carbon dioxide$(CO _2)$, Oxygen$(O _2)$, Ozone$(O _3)$ are part of the atmosphere but chlorine$(Cl _2)$ is not a part of atmosphere.

So answer is B.

One molecule of oxygen is represented by the formula :

  1. $O$

  2. $ O _{2}$

  3. $2O$

  4. $ O _{3}$


Correct Option: B
Explanation:

Oxygen is a chemical element, with the symbol O. Several allotropes, or molecular forms, of it exist, but the three most common in our environment are molecular oxygen, or dioxide, O2

Glass panes usually appear hazy because:

  1. water vapour settling on the tiny dust particles

  2. of chemical reactions

  3. it is the property of all transparent substances

  4. they are old


Correct Option: A
Explanation:

Air contains some gases, water vapours and dust particles that stick to a transparent glass of windows and it appears hazy. 


This is because air is a composition which includes water vapour and some other dust particles that come and rest on the windows which are not wiped. That is why they look hazy.


Hence, option A is correct.

The correct ascending order of gases as per their composition in air is:

  1. oxygen < carbon dioxide < nitrogen

  2. hydrogen < oxygen < nitrogen

  3. nitrogen < hydrogen < oxygen

  4. oxygen < carbon dioxide < hydrogen


Correct Option: B
Explanation:

By volume dry air contains $78.09\%$ Nitrogen, $20.95\%$ Oxygen, $0.93\%$ Argon, $0.04\%$ Carbon dioxide and small traces of other gases.

Ascending order of gases as per their composition in air is-
Hydrogen $<$ Oxygen $<$ Nitrogen

The percentage of nitrogen in air is:

  1. 21%

  2. 0.1%

  3. 54%

  4. 78%


Correct Option: D
Explanation:

The percentage of Nitrogen in air is $78\%$.

The percentage of Oxygen in air is $21\%$
The percentage of Argon in air is $0.93\%$
The percentage of Carbon dioxide is $0.04\%$

Air is regarded as a mixture because:

  1. its pressure may vary

  2. its temperature may change

  3. iis volume changes under different conditions

  4. its composition may vary


Correct Option: D
Explanation:

Air is composed of various gases in different proportions which can be separated using chemical methods.

Which gas has the highest partial pressure in atmosphere?

  1. $CO _2$

  2. $H _2O$

  3. $O _2$

  4. $N _2$


Correct Option: D
Explanation:

Air contains 78% Nitrogen. So, it contributes more no. of moles to partial pressure than any other gas in the atmosphere. So, it has the highest partial pressure. 

Which of the following compound does not exist ?

  1. $H _2$

  2. $He _2$

  3. $N _2O$

  4. $H _2O$


Correct Option: B
Explanation:

The compound compound $ He$ is chemically unreactive (inert) and do not forms compound under normal reaction conditions.$He _2$ does not exist.

A greenhouse gas that absorbs energy and maintains earth's temperature is :

  1. carbon dioxide

  2. nitrogen

  3. ozone

  4. oxygen


Correct Option: A
Explanation:

A greenhouse gas that absorbs energy and maintains earth's temperature is carbon dioxide.

Most abundant constituent of dry air in terms of volume is:

  1. carbon dioxide

  2. helium

  3. nitrogen

  4. oxygen


Correct Option: C
Explanation:

The most abundant gas in the Earth's atmosphere is nitrogen, which accounts for about 78% of the mass of dry air. 

Oxygen is the next most abundant gas, present at levels of 20 to 21%. 
Although humid air seems like it contains a lot of water, the maximum amount of water vapour that air can hold is only about 4%.

Hence, the correct option is $\text{C}$

In desert areas, water vapor content is :

  1. different

  2. higher

  3. low

  4. constant


Correct Option: C
Explanation:

In desert areas, water vapour content is low because deserts are hot areas as there is a lack of water and if there is lack of water than there is lack of water vapour.

Evaporation of water in shade is:

  1. fast

  2. faster

  3. slower

  4. none of these


Correct Option: C
Explanation:

Evaporation of water in shade is slower, as the sun's heat increases the energy of water molecules, and they start moving faster, eventually leading to evaporation when the energy is enough to convert into a gas.

Two forms of oxygen found in the atmosphere are:

  1. water and oxygen

  2. oxygen and carbon dioxide

  3. carbon dioxide and water

  4. oxygen and ozone


Correct Option: D
Explanation:

The two forms of oxygen found in the atmosphere are

  1. Oxygen, $O _2$
  2. Ozone, $O _3$ is found upper layer of the atmosphere.

Which of the following constituent gas is not directly used by the living beings?

  1. Oxygen

  2. Nitogen

  3. Hydrogen

  4. Carbon dioxide


Correct Option: B
Explanation:

Nitrogen gas cannot be used by the human beings directly, breathing pure nitrogen means we're not breathing oxygen, which means that we'll die of oxygen deprivation in a matter of minutes
Hence option B is correct.

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