(i) The valency of chloride ion is -1. Hence the formula becomes YCl4(ii) The valency of oxide ions is -2. Hence the formula becomes YO2(iii) The valency of sulphate ion is -2. Hence the formula becomes Y(SO4)2(iv) The valency of carbonate ions is -2. Hence the formula becomes Y(CO3)2(v) The valency of nitrate ion is -1. Hence the formula becomes Y(NO3)4(vi) The valency of iodide ions is -1. Hence the formula becomes YI4