Question

why size of atom decrease in period? Give reason in short​

Answer 1

In periods the electrons will enter into the same shell as a result the nuclear attraction on valance electron increases so the size atom in period decreases

Answer 2

HERE IS YOUR ANSWER

The numbers of proton increases when we move from left to right in a period.

Due to increase in the numbers of proton the attraction of the nucleus on the electrons present in the outermost shell of atom.

Due to which there is increase in the effective nuclear charge of the atom which reduces the size of the atom