a. \(C{a^{2 + }},{S^{2 - }}\)\( \to \) +2 charge in 1 Ca atom can balance -2 charge in 1 S atom. Hence, formula becomes\(CaS\).
b. \(NH_4^ + ,SO_4^{2 - }\)\( \to \) Since ammonium ion has only +1 charge, we will be needing 2 molecules of ammonium ion to balance -2 charge in sulphate ion. . Hence the formula of compound becomes\({\left( {N{H_4}} \right)_2}S{O_4}\).
c. \(A{l^{3 + }},B{r^ - }\)\( \to \) 3 atoms of Br will be required to balance +3 charge in aluminium ion. . Hence the formula of compound becomes \(AlB{r_3}\).
d. \(N{a^ + },HPO_4^{2 - }\)\( \to \) -2 charge in 1 molecule of hydrogen phosphate can be neutralized by 2 atoms of sodium. . Hence the formula of compound becomes\(N{a_2}HP{O_4}\).
e. \(M{g^{2 + }},PO_4^{3 - }\)\( \to \) Using cross-multiplying method, we can conclude that charge in 3 atoms of Mg will be balancing charge in 2 molecules of phosphate ion. Hence the formula of compound becomes\(M{g_3}{\left( {P{O_4}} \right)_2}\).