JEE Chemistry 2024 Question with Solution

Given: The compounds are $K_2Cr_2O_7$ and $KMnO_4$.

Find: The type of electronic transition responsible for their orange and purple colours.

The solution text states that the colours in both compounds arise from charge transfer transitions and not from $d \rightarrow d$ transitions.

For $K_2Cr_2O_7$, the orange colour is due to charge transfer involving chromium and oxygen.

For $KMnO_4$, the purple colour is due to ligand-to-metal charge transfer involving manganese and oxygen.

Therefore, the colour of both compounds is due to charge transfer transition in both.

The correct option is A.

Note: The solution says "The Correct Option is C", but the detailed working and conclusion clearly identify charge transfer transition in both, which matches option A. Hence the worked explanation is taken as authoritative.

Given: Two coloured compounds, $K_2Cr_2O_7$ and $KMnO_4$.

Find: Whether their colours arise from $d \rightarrow d$ transitions or charge transfer transitions.

The extracted explanation distinguishes two possibilities:

1. Charge transfer transition: an electron moves between ligand and metal orbitals. Such transitions are generally intense and are common in strongly coloured oxoanions.
2. $d \rightarrow d$ transition: an electron moves between d-orbitals of the same metal ion. These transitions are comparatively weak and are usually associated with partially filled d-orbitals in transition metal complexes.

The solution explicitly states:

• The orange colour of $K_2Cr_2O_7$ is due to charge transfer transition.
• The purple colour of $KMnO_4$ is also due to charge transfer transition.

Hence, both compounds show charge transfer transitions as the origin of colour.

Therefore, the correct option is A: Charge transfer transition in both.