___FeCl2 + ___K2S → ___FeS + ___KCl
balance

It would be 1,1,1,2 to make them balance

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