Water gas 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:

The property of hydrogen which distinguishes it from other alkali metals is

Which of the following upon hydrolysis can produce a hydrocarbon that has the same degree of unsaturation as the number of carbon atoms present in the produced hydrocarbon?

Hydrogen gas is prepared by using $C$ (coke) and steam in the presence of $Fe_2O_3/Cr_2O_3$. This process is known as:

Which one of the following is the most abundant element in the universe?