3. Atomic radius goes on increasing down a group.

Ans. 1. For an isolated atom, atomic radius is the distance between the centre of the nucleus of the atom and the outermost shell.

2. Atomic radius goes on increasing down a group because while going down a group a new shell is added.

3. As we move from top to bottom in a group, number of shells increases, Thus, the distance between the outermost electron and the nucleus goes on increasing.

4. As a result of this the atomic size increases in spite of the increased nuclear charge.