Given below are some elements of the Modern Periodic Table. Atomic number of the element is given in the parentheses:
A(4), B(9), C(14), D(19), E(20)
(a) Select the element that has one electron in the outermost shell. Also write the electronic configuration of this element.
(b) Which two elements amongst these belong to the same group? Give reason for your answer.
(c) Which two elements amongst these belong to the same period? Which one of the two has bigger atomic radius?

Explanation

(a) D, the electronic configuration of D(19) is 2,8,8, 1.
(b) A and E belong to the same group as both have the same number of valence electrons, i.e., 2.
(c) A, B and D, E.
A has a bigger atomic radius than B and D has a bigger atomic radius than E.