Question

The product obtained by the dry distillation of coal is:
(A) Natural gas
(B) Water gas
(C) Producer gas
(D) Coal gas

Answer 1

To answer this we should know that dry distillation is the process of heating in absence of air. Dry distillation of solids generally gives us gases. Thus, here dry distillation of coal will give a gas along with other by-products.

Complete step by step solution:
To answer this question, we have to discuss the composition of the gases given to us in the options.
Firstly we have natural gas. It is a naturally occurring hydrocarbon gas and it is also known as fossil gas. It is basically a mixture of methane primarily along with other higher alkanes and also contains a small percentage of nitrogen, carbon dioxide, helium etc.
Then we have water gas. Water-gas consists of a mixture of carbon monoxide and hydrogen. We use it for the removal of carbon monoxide from fuel cell applications. Water-gas is named ‘water’ gas due to the involvement of water steam in its preparation. White-hot hard coal or coke is blasted with steam and it produces carbon monoxide and hydrogen.
Next, we have producer gas. Producer gas is a combustible gas and it is manufactured by blowing steam through hot coke or coal so that the fuel is completely gasified. It consists mainly of carbon monoxide and hydrogen along with nitrogen. It might also contain some amount of carbon dioxide. It is mainly used in large industrial furnaces as a fuel.
And lastly, we have coal gas. It is a flammable fuel made from coal. It is produced upon strongly heating coal in absence of air. We know that organic substances are broken down by heating in absence of air. This process is known as dry distillation. Dry distillation of solids gives us gases and dry distillation of coal gives us coal gas.

Therefore, the correct answer is option (D) coal gas.

Note: When we heat substances like coal, wood, oil shale etc. in absence of air they decompose into gaseous and liquid products including charcoal. Decomposing within a range of 450 to 600 degree Celsius is known as carbonization and decomposing above 900 degree Celsius is known as coking. Coal gas is obtained by gasifying coal and by carbonizing it we obtain coal tar.