Question

Copper forms two oxides. For the same amount of copper, twice as much oxygen was used to form the first oxide than to form the second one. The ratio of the valencies of copper in the first and second oxides is x:y. Then, the value of x+y is:

Answer 1

The first oxide has double the amount of oxygen than in the second, which means that double the negative charge is compensated by same amount of copper, in the first oxide, than in the second oxide.

Therefore, valency of copper in first oxide must be double of the valency of copper in second oxide.

Hence, the ratio is $2:1$ .