Which one of the following metals forms interstitial hydride easily?

The element used for welding metals with high melting points is:

Hydrogen resembles halogens in many respects for which several factors are responsible. Of the following factors,which one is most important in this respect?

Water gas is

The radioactive isotope of hydrogen 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: