Hydrogen reacts with different elements to from variety of hydrides.$1^{st}$ group and $2^{nd}$ group elements form white,crystalline ionic hydride their stability depends upon ionic characters and lattic energy covalent hydride is common type of hydrides transition metals form interstitial hydrides.Which ionic hydride is stable up to its mp?

Question

$\begin{array}{1 1}(a)\;NaH\\(b)\;CaH_2\\(c)\;LiH\\(d)\;BaH_2\end{array}$