The alkali metals form salt-like hydrides by the direct synthesis at elevated temperature. The thermal stability of these hydrides decreases in which of the following orders?

Step-by-step solution

Key Idea : Small anion forms stable compounds with small cation. The thermal stability of alkali metal hydrides decreases as : LiH > NaH > KH > RbH > CsH because the size of cation increases as : Li ⁺ < Na ⁺ < K ⁺ < Rb ⁺ < Cs ⁺