The order of decrease in atomic radii for Be, Na and Mg is

Options

A. `Na gt Mg gt Be`
B. `Mg gt Na gt Be`
C. `Be gt Na gt Mg`
D. `Be gt Mg gt Na`

Answer

A

Explanation

`""_(4)Be=1s^(2)2s^(2)`
`""_(11)Na=1s^(2)2s^(2)2p^(6)3s^(1)`
`""_(12)Mg=1s^(2)2s^(2)2p^(6)3s^(2)`
`""_(4)Be` and `""_(12)Mg` are in a same group and . `""_(11)Na` and `""_(12)Mg` are in a same period.
Atomic radius decreases on moving from left to right in a period and increases on moving from top to bottom in a group. Hence, the order is: Na > Mg > Be.