Question

size of a cation is always smaller than its arom

Answer 1

It is so because when the atom loses electrons ,the no of protons dominates the no of electrons or you can say that the nucleus attracts the electrons , and it causes the cation to shrink ,hence the size of cation decreases .

Answer 2

Cation is positively charged
it is formed by lose of electron from outer most shell
When electron escaped from atom
nuclear charge on rest of electron increase which is attractive in nature
so size of cation is less than atom
Hope this help