i] Atomic radius of hydrogen is 37 pm. Express it in metres.
ii] How does atomic size vary in a group and in a period.

Explanation

(i) 1 pm = `10^(-12)`m.
Atomic radius = `37xx10^(-12)`m.
(ii) In a group atomic size : increases down the group.
In a period atomic size : decreases in moving from left to right.