Question

Na Mg and Al are the elements of the third Period of the modern periodic table having group number 1 ,2 and 13 respectively which one of these element has the (a)highest valency (b) largest atomic radius, and(c) minimise chemical reactivity justify your answer starting the region for each

Answer 1

A.aluminium has highest valency of 3
because it's outermost she'll contains 3 electrons. If it loses those 3, then it can be a noble gas/can have octet configuration
B.Na have larger atomic radius becz in periods from left to right atomic radius goes on decreasing.

Answer 2

a) Highest valency: Aluminium (Al).We know across the period valency is difference.It firstly increases than decreased.
Valency of Na:1
Valency of Mg:2
Valency of Al: 3
b) Largest atomic radius: Sodium (Na).The atomic radii decreases across the period as the effective nucleur charge increases.
c) I don't know this answer.Sorry