Correct Answer – B
The ionic character of MH bond increases from Li to Cs in alkali metals. The corresponding thermal stability decreases. Therefore, the correct decreasing order is as given in option (b)

Correct Answer – C
The tendency to form their hydrides, basic character and stability decreases from `Li` to `Cs` since the electropositive character decreases fro `Cs` to `Li`.

Correct Answer – B
As the size of the alkali metal ion increases, lattice energy decreases and hence, the stability of the corresponding metal hydride decreases.