Ihave 2 electrons in first shell 8 in the second shell and 6 in 3 shell

They did not study the continental drift

Adozen is 1221/12 = 1.751.75 x 12 = 21therefore, 1.75 is the answer.

☆ionisation energy increases across a period from na -> ar☆ionisation energy decreases down a group from li -> fr☆ionic radius decreases across a period from na -> cl☆ionic radius increases down a groupfrom f -> ii hope it clarifies your doubts