CBSE Class 10 Answered

Groups are vertical columns and periods are horizontal rows. So, you see the change as across the period and down the group.

The term reactivity is unclear.

So, if we want to see the metallic character, it increases down the group and decreases across the period. As the size increases, the ionisation energy decreases and hence the electron will be easily released. Since the size increases down the group and decreases along the period, the metallic character increases down the group and decreases across the period.

Or we can also say that the reactivity of metals increases down the group and decreases along the period.

Second property is the non - metallic character.Non - metallic charatcer decreases down the group becauseof decrease in electron affinity due to increase in atomic size. Along a period, non - metallic character increases from left to right due to increase in electron affinity which is due to decrease in atomic size.