BaCl2 solution is added dropwise to a solution that is 2.0x10^-3 M in SO4^2-. Take K_sp(BaSO4) = 1.1x10^-10 and neglect dilution. The minimum [Ba^2+] at which BaSO4 begins to precipitate is

JEE Main levelSingle correct optionDifficulty 2 of 3qa192

$BaCl X_{2}$ solution is added dropwise to a solution that is $2.0 \times 1 0^{- 3} M$ in $SO X_{4} X^{2 -}$ . Take $K_{s p} (BaSO X_{4}) = 1.1 \times 1 0^{- 10}$ and neglect dilution. The minimum $[Ba X^{2 +}]$ at which $BaSO X_{4}$ begins to precipitate is

Precipitation begins when

[Ba X^{2 +}] [SO X_{4} X^{2 -}] = K_{s p}

. So

[Ba X^{2 +}] = 1.1 \times 1 0^{- 10} / (2.0 \times 1 0^{- 3}) = 5.5 \times 1 0^{- 8} M

. The value

K_{s p} \approx 1.0 \times 1 0^{- 5}

is the solubility in pure water, not the threshold here.