CBSE Class 10 Answered

a)      The number of protons increases by one unit from one element to the next element across the period.

b)      The increase in the proton number causes the number of positive charge in the nucleus to increase.

c)      Also, in the same valence shell, there is an increase in an electron one element to the next element across the period.

d)      The increase in the positive and negative charge on the same distance increases nuclei attraction on the valence electron strongly.

e)      Thus, the atomic size/atomic radius decreases across the period.

f)       Size of the atom increases, going down a group due to an increase in number of electron shells, where the inner shell reduce the attractive forces the nucleus and repel the electrons present in the outer shells. Hence the atomic size increases along the group from top to bottom.