Question

Which of the following is the correct chemical formula of magnesium hydroxide?

• A. Mg$(OH{)}_2$
• B. MgOH
• C. MgO$H_2$
• D. $M{g}_{2}O{H}_2$

Answer 1

The correct option is A Mg$(OH{)}_2$

For polyatomic ions like ${OH}^{-}$, the formula of ion is enclosed ​ in a bracket and the number of ions is written outside the bracket.

Valency of $M{g}^{2+}$ ion = 2
Valency of ${OH}^{-}$ ion = 1

Symbol	Mg	OH
Valency	2	1

Upon criss-crossing the valencies, we get the formula of the compound as Mg$(OH{)}_2$.