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

(N/A) Non-stoichiometric hydrides are metallic hydrides where the ratio of hydrogen to metal is not a simple integer,and they do not follow the law of constant composition. These are often hydrogen-deficient. Examples include $LaH_{2.87}$ and $PdH_{0.6-0.8}$.
Alkali metals (Group $1$) form ionic or saline hydrides (e.g.,$LiH, NaH$),which are stoichiometric. They do not form non-stoichiometric hydrides because they have a strong tendency to form ionic bonds by transferring electrons to hydrogen,rather than forming interstitial metallic structures.