Question 5
What is the chemical formula of lithium fluoride?
The right answer is the one marked above.
LiF. Lithium has a valency of 1 and fluorine a valency of 1, so one atom of each is all that is needed.
Crossing over gives Li1F1, and a subscript of 1 is never written. Take care not to leave it as Li2F2 either — a formula is always written in its simplest ratio.