Another form of solid carbon dioxide observed at high pressure is an amorphous glass-like solid. This form of glass, called carbonia, is produced by supercooling heated $C{O} _{2}$ at extreme pressure ($40 48  GPa$ or about $400,000$ atmospheres) in a diamond anvil.
This discovery confirmed the theory that carbon dioxide could exist in a glass state similar to other members of its elemental family, like silicon (silica glass) and germanium dioxide.

Carbon dioxide gas is fairly soluble in water.
Aerated water is a solution of $CO _2$ in water under pressure.

Carbon dioxide is a colourless, odourless and linear molecule. Its structure can be represented as $O=C=O$ The $O-C-O$ bond angle is 180 $^o$. The carbon atom is $sp$ hybridised.

Supercritical carbon dioxide is a fluid state of carbon dioxide where it is held at or above its critical temperature and critical pressure. Carbon dioxide usually behaves as a gas in air at standard temperature and pressure (STP), or as a solid called dry ice when frozen. If the temperature and pressure are both increased from STP to be at or above the critical point for carbon dioxide, it can adopt properties midway between a gas and a liquid.

 Gaseous or liquid carbon dioxide, stored under pressure, will form dry ice through an auto-refrigeration process if rapidly de-pressured.

Atomic number = number of protons = 8
Number of neutrons = 8
Mass number = number of protons + number of neutrons
So mass number of oxygen = 16

Dissolved air has a higher percentage of oxygen as compared to ordinary air. Air dissolved in water contains 36% oxygen as compared to 21% in air. This is because oxygen in the air has a higher solubility than other elements in air and also there is hydrogen bonding between water and oxygen that increases its solubility.

Oxygen is neutral to litmus paper.

Oxygen is colourless and odourless gas.

$2NO+O _2\longrightarrow 2NO _2$

Oxygen is a supporter of combustion. Combustion does not take place without oxygen.

When oxygen reacts with alkaline pyragallol solution,dark brown colour is seen and it forms a complex compound.

The chemicals used for testing oxygen are nitric oxide and alkaline pyragallol solution.

When $NO$ mixes with oxygen, reddish brown fumes of $NO _2$ appears.$2 NO _{(g)} + O _{2(g)}\rightarrow 2NO _{2(g)}$

Oxygen is a supporter of combustion. Introducing the burning splint will rekindle it.

Dissolved oxygen means the  free or  non-compound oxygen present in water or in  other liquids. Dissolved oxygen is important to many forms of life including fish, bacteria and plants. These organisms use oxygen in respiration, similar to organisms on land. Fishes obtain oxygen for respiration through their gills, while plant life and phytoplankton require dissolved oxygen for respiration when there is no light for photosynthesis.

So the given statement If dissolved oxygen is not present, the aquatic life would die.

$H _2S$ burns completely in the presence of oxygen as:

Characteristic test for oxygen ($O _{2}$) can be performed on the basis that oxygen supports burning. Therefore if we bring a burning candle near the source of oxygen, the intensity of the flame increases.

Carbon dioxide is colorless. At low concentrations, the gas is odorless. At higher concentrations it has a sharp, acidic odor. At standard temperature and pressure, the density of carbon dioxide is around $1.98  {kg}/{{m}^{3}}$, about $1.67$ times that of air.

Carbon dioxide gas does not allows the earth to radiate out heat rapidly. So, it is one of the green house gas.

Carbon dioxide exists in Earth's atmosphere as a trace gas at a concentration of about $0.04$ percent $\left(400   ppm\right)$ by volume. A trace gas is a gas which makes up less than $1$% by volume of the Earth's atmosphere.

Burning of carbon is an exothermic reaction because heat is evolved in this reaction.
$C + O _2 \rightarrow CO _2 + $ heat
The enthalpy change is negative.