Answer:
The litmus paper will turn blue; Ca(OH)₂
Step-by-step explanation:
Limewater is a dilute aqueous solution of calcium hydroxide.
Ca(OH)₂(aq) ⟶ Ca²⁺(aq) + 2OH⁻ (aq)
Limewater contains hydroxide ions. They cause the limewater to be basic.
Litmus is a mixture of dyes extracted from lichens. They are weak acids with complicated formulas.
Let's just write the formula for litmus as HLit.
The hydroxide ions from limewater react with the H of litmus to form a salt — the base form — and water.
HLit + OH⁻ ⟶ Lit⁻ + H₂O
acid form base form
red blue
The base form of litmus is blue, so
Red litmus turns blue in the presence of limewater.