The alkali metals from salt-like hydride by the direct synthesis at elevated tempeature. The thermal stability of these hydrides decreases in which of the following orders? (AIPMT 2008)

The thermal stability of alkali metal hydrides de-creases down the group. As the counter hydrogen anion is smaller, larger the cation larger the instability. Hence, the correct order for the thermal stability is as follows LiH > NaH > KH > RbH > CsH.