WBJEE 2025 Physics and Chemistry Papers

First, calculate the moles of HgO :
n(HgO)=‌

0.217g

217g∕mol

=0.001‌mol
According to the reaction:
HgO+4I−+H2O→HgI42−+2OH−
Each mole of HgO produces 2 moles of hydroxide ions (OH−). So, the moles of OH− formed are:
n(OH−)=2×0.001=0.002‌mol
Next, these hydroxide ions are titrated with HCl . The reaction between HCl−and OH−is:
HCl+OH−→H2O
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:
0.2L=200‌mL
Thus, 200 mL of 0.01 M HCl is required at the equivalence point.
The correct answer is Option B: 200 mL .