Steel being an alloy of metals, it has free electrons in its atoms. They start moving along with the heat flow and help in the conduction of heat. All metals are good conductors. The other three being non-metals, do not have free electrons. Hence they are bad conductors

All metals are good conductors while non-metals are bad conductors of heat.

When we touch a steel rod and a paper simultaneously in winter, we feel the rod is comparatively colder because steel being a good conductor of heat, heat from our hand flows to steel but there is no transfer of heat from our hand to paper as it is an insulator of heat. So we don't feel cold when we touch a paper but we do when we touch a steel rod.

A thermal conductor is a material that allows energy in the form of heat, to be transferred within the material, without any movement of the material itself. Eg. Metals.

Metals are generally good conductors of heat.
Non - metals are poor conductors of heat.

Water is the poor conductor among all. As it is liquid and liquids generally have low heat conductivity than solids. Tighter the molecules are held, more the vibrational energy can transfer between them, heat is no more than vibrating molecules. If we talk about steam, its molecules are less tightly held. But it's important to note that we are talking here of heat conductivity not convection or radiation and contact surface area with heat source.

Woollen clothes effectively separate the body from surrounding air by entrapping a layer of air.
Since both wool and air are bad conductors of heat on varying levels, it creates separation that keeps bodies warm.

Conductors allow heat to pass through them through vibration of the molecules.

Glass is a bad conductor of heat hence the heat from the upper part of the glass tube will not transfer easily to the lower part. Having said that, even wax is a bad conductor of heat and won't melt easily. 

Silver is the best conductor of heat among the given options.

When the hot tea is poured into the glass tumbler one side of the glass expands while the other side doesn't. Since glass is not a good conductor of heat, it breaks.

Metals are good conductors of heat hence a person might get his fingers injured if he holds the hot plate. 

Cork is a bad conductor of heat rest are good conductors

Insulators are  through which heat cannot pass easily.

Asbestos is an insulator rest are good conductors of heat

Silver is a good conductor of heat rest are bad conductors

Ebonite is a very good insulator while mercury, silver and copper are examples of conductors.

Metals have much lower specific heat than water because metals require smaller amount of energy to raise their temperature than water .

Usually, good conductors of heat are also good conductors of electricity. However, this is not always true. One of the exceptions is mica. Mica is good conductor of heat but bad conductor of electricity.

In conduction, heat is transferred by the vibrations of molecules. The density of conductors is large, it means molecules are close to each other, because of that they can easily transfer the heat quickly through the whole conductor, therefore unit mass of conductors require small heat to raise their temperature through $1^{o}$ i.e. conductors have very low specific heat. 

$Q=ms\Delta T$,

Conductors have very low specific heat capacity (c) , therefore heat required (Q) to raise their temperature to a certain range is also less by the following relation: $Q\propto c$

Sulphur, Phosphorus, Wood are non-conductors of electricity due to no presence of free electrons in outermost shell.

Conductors can easily conduct electricity because they are loosely bound to the nucleus and they are not engaged in chemical bonding. Conductors have free electrons.

In conductors, electrons can flow because their electrons are free and mobile metals have free electrons present in outermost orbit i.e. they are mobile in nature. This is the fact due to which they could produce electricity.

An electrical insulator is a material whose internal electric charges do not flow freely because of extremely high resistance. Very little electric current will flow through it under the influence of an electric field.

Metals have free electrons which can move from atom to atom easily, whereas non-metals do not, their electrons are 'bound' meaning they cannot move easily. That's why metal are usually good conductors than non-metals.

Pure water or distilled water doesnot conduct electricity but tap water, rain water or sea water conduct electricity. For electricity to travel through a liquid movement of charge must take place through the liquid. In tap water, rain water or sea water, there are impurities such as salt of $Na,Mg \; and \; Ca$. They behave as the charge carriers for conduction of electricity. But in distilled water there are no impurities i.e. no ions. There are only neutral water molecules. So, distilled water doesnot conduct electricity.

Copper is usually used for copper wiring because copper conducts electricity. Because electrical conductivity of copper is good enough and it is cheap too. So it is used in wiring.

Insulators are used in circuits, as they don't conduct electricity, they are used for insulation of wire, switches, plugs, etc. So that circuit could be made shock free and safe to touch.

Electrical plugs are made up of plastic because plastic protects people from electricity. As we know that plastic is an electrical insulator readily available and cheap. So as to make the plugs shock free, they are made up of plastic.

Electrical wiring is usually covered with layer of plastic to make it safe. As we know that plastic is an electrical insulator and it is readily available and cheap. So as to insulate the electricity carrying wire, to make it shock free. It is covered with layer of plastic.

Materials that allow electrons to flow through them are known as conductors because they consist of free electrons.

Pots and pans are NOT example of insulator, they are conductors of heat, if it was not so; they could not be used for cooking of food. And they are used for cooking; so they are conductors.

Scissors made of iron could be used to complete an electrical circuit. As iron is a metal and conductor so can conduct electricity easily. And others are non-metals. So they could not conduct electricity and can't complete the circuit.

Pure water consists of no impurities; impurities such as salts of $Mg,Ca,Na$ are behaving here as charge carriers but since they are not present; there are no ions. They are neutral water molecules. So pure water do not conduct electricity.

Mud is a bad conductor of heat. It does not allow the heat to transfer from house to atmosphere in winter and atmosphere to house in summer.

Heat spontaneously flows from a hotter to a colder body. The rate at which energy is conducted as heat is a function of temperature. Hence heat flows as a result of temperature.

We know that the heat content is proportional to the mass and specific heat capacity of the substance as well as temperature. As both the spheres are of the same material and are at the same temperature, heat content will be dependent on mass only.

$ m = \rho \times v$

where $ \rho $ is the density of the sphere and $v$ the volume.

And $ v $ = $ \dfrac {4 \pi r^3}{3} $

The given radius ratio is $ 1:2 $.

Hence heat contents ratio is in the ratio $1:8$

In conduction, heat is transferred by the vibrations of molecules. The density of metals is large, it means molecules are close to each other, because of that they can easily transfer the heat quickly through the whole conductor, besides this metals have electron sea, due to smaller size of electrons compared to metal ions, electrons can easily pass through the space between ions, thus transfer the heat. Therefore are good conductors of heat.

The specific heat capacity of a substance is the amount of heat required to raise the temperature of unit mass of substance through $1^{o}$.

Good conductors of heat are substances through which heat can pass easily.

Substances which don't allow heat to easily pass through them are known as insulators. Insulators have crystal structure of molecules, molecules are far from each other, compared to conductors. Hence, they cannot pass the heat easily through them, besides this insulators don't have free electrons to pass heat more quickly. Therefore, unit mass of an insulator requires more heat to raise its temperature by $1^{o}$ i.e. specific heat capacity of insulators is very high or we can say they need more heat per degree rise in temperature.

Substances which allows heat to pass through them easily are known as Conductors.

Substances which don't allow heat to easily pass through them are known as insulators. Insulators have crystal structure of molecules, molecules are far from each other, compared to conductors. Hence they cannot pass the heat easily through them, besides this insulators don't have free electrons to pass heat more quickly.

If needle is burnt then the heat transfer through the whole length of needle is faster, because needle (metal), being a good conductor of heat, heat passes along the whole length by conduction, in which heat is transferred by one atom to another connected atom quickly.