Non- metallic character increases from left to right in a period because effective nuclear charge increases from left to right in a period. Due to this effective nuclear charge, the electronegativity increases and the tendency of gaining electrons also increases. So non- metallic character increases from left to right in a period.

Note-

(i) Effective nuclear charge is defined as the charge per unit volume.

(ii) From left to right in a period, the effective nuclear charge increases because charge increases from left to right due to increment of proton. But the size remains same because number of shells remains same from left to right in a period.

(iii) From top to bottom in a group, the effective nuclear charge decreases because charge increases down a group due to increment of proton and the size of elements also increases due to increment in shells.