Question

why is k more reactive than Na

Answer 1

potassium is more reactive than sodium because it loses its electrons faster, it has less force of attraction between nucleus &electron

Answer 2

in potassium, the outermost electron is better shielded from the attractive force of the nucleus. It follows, therefore, that this outermost electron is more easily lost than it is in sodium, so potassium can be converted to ionic form more readily than sodium. Hence, potassium is more reactive than sodium