The following table shows the position of five elements A, B, C, D, and E in the modern periodic table.

Answer the following giving reasons: 

(i) Which element is a metal that has the valence as one? 

(ii) Which element is a noble gas? 

(iii) Out of D and E which element has a larger atomic radius?

(i) A element is a metal with valency 1. It is because it is on the left side of the table in group 1.
(ii) Element C is the noble gas. Therefore this element is least reactive.
(iii) Element D has a larger atomic radius.
As we move from left to right across a period, the atomic radius decreases due to the increase in the effective nuclear charge.