Metal hydride on treatment with water gives

The nucleus of tritium contains

The most abundant element in the universe is

How can $D_2O$ be prepared from water? Mention the physical properties in which $D_2O$ differs from $H_2O$. Give at least three reactions of $D_2O$ showing the exchange of hydrogen with deuterium.

Given below are two statements:
Statement $I$ : Nickel is being used as the catalyst for producing syn gas and edible fats.
Statement $II$ : Silicon forms both electron rich and electron deficient hydrides.
In the light of the above statements,choose the most appropriate answer from the options given below:

What do you understand by the term "non-stoichiometric hydrides"? Do you expect this type of the hydrides to be formed by alkali metals? Justify your answer.