Question

why does the atomic size decrease down the group​

Answer 1

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A higher effective nuclear charge causes greater attractions to the electrons, pulling the electron cloud closer to the nucleus which results in a smaller atomic radius. Down a group, the number of energy levels (n) increases, so there is a greater distance between the nucleus and the outermost orbital.

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Answer 2

Answer:

THE NEW SHELLS ARE ADDED

Explanation:

On moving down the group, new shells are being added. The nuclear charge is not enough to reduce the size enough. So the radius increases as we move down the group