The ionization enthalpies of the alkali metals decrease down the group from `Li` to `Cs` because :

Options

A. The effect of increasing size outweighs the increasing nuclear charge.
B. The outermost electron is very well screened from the nuclear charge.
C. Both `(a)` and `(b)`.
D. none of the above

Answer

C

Explanation

The ionization enthalpies of the alkali metals decrease down the group from `Li` to `Cs` because the increase in size overweighs the increase in nuclear charge. As a result, the attraction between valence shell electrons and nucleus decreases down the group and therefore, the ionisation enthalpies decrease from` Li` to `Cs`.