\( 20 \, \text{mL} \) of calcium hydroxide was consumed when it was reacted with \( 10 \, \text{mL} \) of unknown solution of \( \mathrm{H_2SO_4} \). Also \( 20 \, \text{mL} \) standard solution of \( 0.5 \, \mathrm{M} \) \( \mathrm{HCl} \) containing \( 2 \) drops of phenolphthalein was titrated with calcium hydroxide, the mixture showed pink colour when burette displayed the value of \( 35.5 \, \text{mL} \) whereas the burette showed \( 25.5 \, \text{mL} \) initially. The concentration of \( \mathrm{H_2SO_4} \) is: _______ \( \mathrm{M} \). (Nearest integer)
