Question

The solution of calcium oxide turns red litmus blue.
A. True
B.False

Answer 1

Calcium oxide is a basic oxide its formula is $CaO$ .It reacts with water to form calcium hydroxide$Ca{\left( {OH} \right)_2}$ also called slaked lime which is a base because it release $O{H^ - }$ ion in the aqueous solution. So we can say that base is a compound that increases concentration of $O{H^ - }$ in the solution.

Complete answer:
Before discussing the solution of calcium oxide turns red litmus to blue. We have to get an idea about what actually is a base. In general bases are bitter in taste and turn red litmus to blue. The definition bases are given by various theories; Arrhenius theory, Bronsted-lowry and Lewis theory.
Arrhenius theory: According to the Arrhenius theory base is a substance that dissociates to form $O{H^ - }$ in aqueous solution.
Bronsted-lowry theory: According to this theory, base is a substance that receives a proton from an acid or any substance that removes a proton from an acid.
Lewis theory: According to this theory base is a substance that donates electron pairs.
Bases oxide are oxides that show basic properties that react with water to form a base and when react with acid to form salt and water.
In case of Calcium hydroxide $\left( {CaO} \right)$ it reacts with water to form Calcium hydroxide$Ca{\left( {OH} \right)_2}$ which is a base because it releases the $O{H^ - }$ ion in the aqueous solution. The reaction involved is
$CaO + {H_2}O \to Ca{\left( {OH} \right)_2}$
The reaction shows that $CaO$ basic oxide because it forms $Ca{\left( {OH} \right)_2}$ which is a base which we already discuss that’s why the solution of $CaO$ turns red litmus blue.

So the given statement is true.

Note:
Acid turns blue litmus to red whereas the base solution turns red litmus to blue. We can also determine whether a solution is base or acid by $pH$ paper if it shows $pH$ above $7$ then it is a base and if it shows $pH$ less than $7$ then it is acid.$pH$ Range of $pH$ paper is $1$ to$14$ . When $pH$ is equal to $7$ then it is neutral.