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i) Sodium is an ionic compound made up of sodium ions and oxide ions. The sodium ion has a valency or charge of 1+ where is oxide Ion has a valency or charge of 2-



Na O
1+ 2- (cross over valencies)

Formula: Na₂O

Hence, the formula of sodium oxide is Na₂O.


ii) Aluminium chloride is an ionic compound made up of aluminium ions and chloride ions. Aluminium Ion has a valency of 3+ whereas chloride Ion has a valency of 1-.



Al Cl
3+ 1- (cross over valencies)

Formula: AlCl₃

Hence, the formula of aluminium chloride is AlCl₃.


iii) Sodium sulphide ionic compound made up of sodium ions and sulphide ions. Sodium Ion has a valency of 1+ ion has a valency of 2-



Na S
1+ 2- (cross over valencies)

Formula: Na₂S

Hence, the formula of sodium sulphide is Na₂S.

iv) Magnesium hydroxide is an ionic compound made up of magnesium and Hydroxide ions. Magnesium iron has a valency of 2+ and Hydroxide has a valency of 1-



Mg OH
2+ 1- (cross over valencies)

Formula: Mg(OH)₂

Hence, the formula of magnesium hydroxide is Mg(OH)₂.