JEE Chemistry 2024 Question with Solution

Given: Five statements about chromate, dichromate, manganate and oxides of transition metals are to be checked.

Find: Which statements are correct.

Evaluate each statement one by one:

1. Statement A: Chromate ion $\text{CrO}_4^{2-}$ is not square planar. It has tetrahedral geometry. So A is incorrect.

2. Statement B: Dichromate is prepared from chromate on acidification.

So B is correct.

3. Statement C: Green manganate ion $\text{MnO}_4^{2-}$ is paramagnetic, not diamagnetic, because it has unpaired electron(s). So C is incorrect.

4. Statement D: Dark green $K_2\text{MnO}_4$ disproportionates in neutral or acidic medium to give permanganate.

So D is correct.

5. Statement E: As oxidation number of transition metal increases, polarising power increases and the oxide shows more covalent character. Hence ionic character decreases. So E is correct.

Therefore, the correct statements are B, D and E only.

Given: The options list five independent statements.

Find: The set of true statements.

• $\text{CrO}_4^{2-}$ is tetrahedral, therefore statement A is false.
• Dichromates are obtained from chromates by acidification, so statement B is true.
• Green manganate is paramagnetic with one unpaired electron as stated in the solution source, so statement C is false.
• Statement D is true because manganate disproportionates to permanganate in suitable medium.
• Statement E is true because higher oxidation state increases covalent character and decreases ionic character of oxides.

Hence the correct option set is B, D, E.