Periodic Table, Periodic Properties and Variations of Properties — Question 8

(i) On moving from left to right in the third period, the chemical reactivity of elements first decreases until silicon as the tendency to lose electrons deceases and then starts to increase from phosphorus to chlorine, as the tendency to gain electrons increases.

(ii) Chemical reactivity in metals increases on going down the group, but in non-metals it decreases on going down the group.
(a) As group IA (1) contains metals, hence, chemical reactivity increases on going down the group IA (1).
(b) As group VIIA (17) contains non-metals, hence, chemical reactivity decreases on going down the group VIIA (17).