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.

(N/A) Non-stoichiometric hydrides are hydrogen-deficient compounds formed by the reaction of dihydrogen with $d$-block and $f$-block elements. These hydrides do not follow the law of constant composition. For example: $LaH_{2.87}$, $YbH_{2.55}$, $TiH_{1.5-1.8}$ etc.
Alkali metals form stoichiometric hydrides. These hydrides are ionic in nature. Hydride ions have comparable sizes $(208 \text{ pm})$ with alkali metal ions. Hence, strong binding forces exist between the constituting metal and hydride ion. As a result, stoichiometric hydrides are formed.
Alkali metals will not form non-stoichiometric hydrides.