Which is the lightest gas?

Which of the following processes produces hydrogen with the highest purity $(99.9\%)$?

Which of the following is radioactive?

Given below are two statements :
Statement-$I$: The process of producing syn-gas is called gasification of coal.
Statement-$II$: The composition of syn-gas is $CO + H_2$ ($1 : 1$ ratio).
In the light of the above statements,choose the most appropriate answer from the options given below:

The sum of the total number of neutrons present in protium, deuterium, and tritium is:

Given below are two statements,one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A:$ Isotopes of hydrogen have almost same chemical properties,but difference in their rates of reaction.
Reason $R:$ Isotopes of hydrogen have different enthalpy of bond dissociation.
In the light of the above statements,choose the most appropriate answer from the options given below: