Question

1. the formula for calcium oxide is

a ca₂o₂
b cao₂
c ca₂o
d cao

1. the formula for magnesium hydroxide is

a mgoh
b mg(oh)₂
c mg₂oh
d mg₂(oh)₂

Explanation:

3.

Step1: Determine the valency of calcium and oxygen

Calcium (\(Ca\)) has a valency of \(+ 2\), and oxygen (\(O\)) has a valency of \(-2\).

Step2: Cross - multiply the valencies

Using the criss - cross method, for \(Ca^{2+}\) and \(O^{2 -}\), the formula is \(CaO\) (the ratio of \(Ca:O = 1:1\) after simplifying the cross - multiplied values).

4.

Step1: Determine the valency of magnesium and hydroxide ion

Magnesium (\(Mg\)) has a valency of \(+2\), and the hydroxide ion (\(OH^{-}\)) has a valency of \(-1\).

Step2: Cross - multiply the valencies

Using the criss - cross method, for \(Mg^{2+}\) and \(OH^{-}\), we get \(Mg(OH)_2\) (since we need two \(OH^{-}\) ions to balance the \(+ 2\) charge of \(Mg^{2+}\)).

Answer:

1. D. \(CaO\)
2. B. \(Mg(OH)_2\)