Question

In the formula X2O5, the symbol X could represent an element in Group
(1) 1 (3) 15
(2) 2 (4) 18

Answer 1

Answer: (3) 15

Explanation: We criss-cross down the oxidation numbers to get the subscripts for the correct formulas. That means the X has an oxidation number of 5. The element with the + oxidation number is always written first so it is +5. Of the groups names, only group 15 has +5 as an oxidation number.