20mL of calcium hydroxide was consumed when it was reacted with...

Titration principle is ${N}_{1}{V}_{1} = {N}_{2}{V}_{2}$

N = Normality

V = Volume of solution

${M}_{1}{V}_{1}{n}_{1} = {M}_{2}{V}_{2}{n}_{2}$

M = molarity

n = Valence factor of acid or base

As pink colour is obtained on consumption of $10ml$ of $Ca ( OH{)}_{2},$ we have

$20 \times 0 . 5 \times 1 = 10 \times M \times 2$

Molarity of $Ca ( OH{)}_{2} = \dfrac{10}{20} = \dfrac{1}{2}M$

Also, moles of $Ca ( OH{)}_{2} = mm$ of ${H}_{2}{SO}_{4}$

$\dfrac{1}{2} \times 20 = 10 \times M$

Molarity of ${H}_{2}{SO}_{4} = 1M$