Which of the following statements about the periodic trend of atomic radius is/are true? i. atomic radius decreases from left to right across a period because zeff increases. ii. atomic radius increases from left to right across a period because the number of valence electrons increases. iii. atomic radius increases from top to bottom in a group because the number of electron shells increases. 1. i only 2. i and iii only 3. ii and iii only 4. ii only

2. I and III only

Explanation:

I. Atomic radius decreases from left to right across a period because Zeff increases.

Atomic radius decreases as we move from left to right because here the effective charge of the nucleus will attract the electron cloud due to which all electrons will come closer as we move from left to right

III. Atomic radius increases from top to bottom in a group because the number of electron shells increases.

As we move from top to bottom then due to increase in the number of orbitals the effective charge of the nucleus will decrease and hence the atomic radius will also increase