Question

The correct arrangement of decreasing order of atomic radius among `Na, K, Mg` and `Rb` is
A. `Rb gt Na gt N gt Mg`
B. `K gt Rb gt Na gt Mg`
C. `Rb gt K gt Na gt Mg`
D. `Mg gt Rb gt K gt Na`

Answer 1

Correct Answer - C
`Na, K` and `Rb` are of group `1` elements and size increase down the group `1` elements `(darr)`.
`Na` and `Mg` are of group `1` and `2` elements respectively but both belong to `3rd` period. Along the period size decreases `(rarr)`, i.e. size of `Na gt Mg`.
Hence the order of sizes is