Question

Whose atomic size is more .Sodium ion or magnesium ion.Why?

Answer 1

The atomic size in decreases while going from left to right in a modern periodic table.
Hence the atomic size of sodium is more than magnesium

Answer 2

$hi \: mate \\ hope \: this \: help \: you \\ sodium \: has \: larger \: atomic \: size \\ because \: electronic \: configuration \: of \: \: sodium \: \\ is \: 1 {s}^{2} \: 2{s}^{2} \: 2{p}^{6} \: 3{s}^{1} \: and \: of \\ magnesium \: is \: 1{s}^{2} \: 2 {s}^{2} \: 2{p}^{6} \: 3{s}^{2} \\ in \: magnesium \: the \: effective \\ nuclear \: charge \: is \: more \: than \: sodium \: so \\ the \: size \: of \: sodium \: is \: larger$