JEE Chemistry 2026 Question with Solution

Given: A mixture $X$ is prepared by dissolving $0.4$ mol each of $[\mathrm{Co(NH_3)_5SO_4}]Br$ and $[\mathrm{Co(NH_3)_5Br}]SO_4$ to make $4$ L solution.

Find: Which statement about precipitates $Y$ and $Z$ is correct.

Only counter ions take part in precipitation reactions; ligands inside the coordination sphere do not.

So this complex gives free $\mathrm{Br}^-$ as counter ion.

So this complex gives free $\mathrm{SO_4}^{2-}$ as counter ion.

Since the total volume is $4$ L, in $2$ L of solution the moles of each salt are half:

When $2$ L reacts with excess $\mathrm{AgNO_3}$, only free $\mathrm{Br}^-$ forms precipitate $\mathrm{AgBr}$.

Hence, moles of $Y = \mathrm{AgBr}$ formed are $0.2$ mol.

When the other $2$ L reacts with excess $\mathrm{BaCl_2}$, only free $\mathrm{SO_4}^{2-}$ forms precipitate $\mathrm{BaSO_4}$.

Hence, moles of $Z = \mathrm{BaSO_4}$ formed are $0.2$ mol.

Therefore, the correct option is C and $0.2$ mol of $Z$ is formed.