Elements A and B form two new compounds. In compound I, 2 grams of A is combined with 4 grams of B. In compound II, 4 grams of A is combined with 12 grams of B. If the formula of compound I is A2B, what is the formula of compound II?

Answer 1

They tell you that compound A2B has twice the mass of B as A. That requires that element A have 1/4 the mass of B.

For a compound to have three times more B than A (my mass), the formula must be A4B3, or (A4B3)n, where n is an integer