WBJEE 2025 Physics and Chemistry Papers

First, calculate the moles of HgO :$n(\mathrm{HgO})=\frac{0.217\ \mathrm{g}}{217\ \mathrm{g}/\mathrm{mol}}=0.001\ \mathrm{mol}$According to the reaction:$\mathrm{HgO}+4\ \mathrm{I}^{-}+\mathrm{H_2O}\rightarrow\mathrm{HgI}_4^{2-}+2\ \mathrm{OH}^{-}$Each mole of HgO produces 2 moles of hydroxide ions $(\mathrm{OH}^{-})$. So, the moles of $\mathrm{OH}^{-}$ formed are: $n(\mathrm{OH}^{-})=2\times 0.001=0.002\ \mathrm{mol}$Next, these hydroxide ions are titrated with HCl . The reaction between $\mathrm{HCl}^{-}$and $\mathrm{OH}^{-}$is:$\mathrm{HCl}+\mathrm{OH}^{-}\rightarrow\mathrm{H_2O}$ This reaction occurs in a 1:1 mole ratio. Therefore, 0.002 moles of HCl are needed to neutralize the hydroxide produced.Given that the concentration of HCl is 0.01 M , the volume of HCl required is calculated by: Converting liters to milliliters:$0.2\ \mathrm{L}=200\ \mathrm{mL}$Thus, 200 mL of 0.01 M HCl is required at the equivalence point.The correct answer is Option B: 200 mL .