Choose the correct answer. 1. A bad smalling gas is mixed with cooking gas.so that; (a)cooking gas burns better in presence of this gas (b)it becomes odouries after buring(C)it helps detect leakage of cooking gas(D)a preevents leakage of cooking gas.

(C) This question is based around methane which is odourless and colourless, certainly when compared with 'town gas' its predecessor. Thus when local gas supplies were changed over from town gas to methane (usually from gas fields) a sulfide or mercaptan was added. You might be interested to know that the addition is a legal requirement in many countries; in the UK, USA and Canada there must be enough 'smell' added to be able to detect about 1% in the air whereas in Japan it must be enough to smell 0.1%.

To choose the correct answer, let's break down each option and determine the correct one:

(a) Cooking gas burns better in the presence of this gas: This is not the correct answer because the statement does not imply that the cooking gas burns better due to the presence of the bad smelling gas. The presence of the bad smelling gas does not enhance the burning efficiency of cooking gas.

(b) It becomes odorless after burning: This is also not the correct answer because the statement indicates that the bad smelling gas is mixed with cooking gas, but it does not mention anything about the odor changing after burning.

(c) It helps detect leakage of cooking gas: This is the correct answer. The bad smelling gas, often referred to as a "mercaptan," is purposely mixed with cooking gas (usually natural gas) to give it a distinctive smell. This smell makes it easier to detect any leakage of the cooking gas, which is essential for safety purposes.

(d) It prevents leakage of cooking gas: This is not the correct answer. The statement does not imply that the bad smelling gas prevents the leakage of cooking gas.

Therefore, the correct answer is (c) It helps detect leakage of cooking gas.