Answer the question no.17

Dear student, (1) Group 1 elements ( represented by X) have valency 1 and oxygen has valency 2. By criss-cross method the formula of oxide with group 1 elements is X2O. (2) Group 13 elements have valency 3. Halogens have valency 1. Thus the formula of group 13 halides can be represents as MX3 (M represents group 13 element and X represents halogen). (3) Group 15 elements have a valency of -3. So they combine with hydrogen to form MH3. Thanks and regards