Question

The second I.P for alkali metals shows a jump while the third I.P for alkaline earth metal shows a jump.

Answer 1

After losing 1 electron, the alkali metals obtain noble gas configuration and become highly stable. And alkali earth metals obtain alkali metals configuration.

Hence the second I.P. of alkali metals becomes very high due to its stability.
And the second I.P. of alkali earth metal is low as they can easily lose 1 electron to gain noble gas configuration.