Which of the following compounds give colour due to charge transfer?

Options

A. `K_(2)Cr_(2)O_7`
B. `KMnO_(4)`
C. `[Fe(H_(2)O)_(5) NO]SO_(4)`
D. `CaCl_(2)`

Answer

To determine which of the following compounds give color due to charge transfer, we will analyze each compound based on their oxidation states and the nature of the charge transfer involved.

### Step 1: Analyze K2Cr2O7
1. **Determine the oxidation state of Chromium (Cr)**:
- Oxygen has an oxidation state of -2.
- In K2Cr2O7, there are 7 oxygen atoms: \(7 \times (-2) = -14\).
- Let the oxidation state of Cr be \(x\). The equation becomes:
\[ 2x + (-14) + 2(1) = 0 \implies 2x - 12 = 0 \implies 2x = 12 \implies x = +6 \]
- Thus, Cr is in the +6 oxidation state.

2. **Determine the electronic configuration**:
- Chromium in +6 state has a D0 configuration (no d electrons).

3. **Charge transfer mechanism**:
- The ligand (O2-) has filled π orbitals, and the empty T2g orbitals of Cr can accept electrons.
- This leads to ligand-to-metal charge transfer (LMCT), resulting in intense red color.

### Step 2: Analyze KMnO4
1. **Determine the oxidation state of Manganese (Mn)**:
- Oxygen has an oxidation state of -2.
- In KMnO4, there are 4 oxygen atoms: \(4 \times (-2) = -8\).
- Let the oxidation state of Mn be \(y\). The equation becomes:
\[ y + (-8) + 1 = 0 \implies y - 7 = 0 \implies y = +7 \]
- Thus, Mn is in the +7 oxidation state.

2. **Determine the electronic configuration**:
- Manganese in +7 state also has a D0 configuration.

3. **Charge transfer mechanism**:
- Similar to K2Cr2O7, the filled π orbitals of O2- can transfer electrons to the empty d orbitals of Mn.
- This results in ligand-to-metal charge transfer (LMCT), leading to intense purple color.

### Step 3: Analyze Fe(H2O)5NO(SO4)
1. **Determine the oxidation state of Iron (Fe)**:
- In this complex, Fe is in the +2 oxidation state when reacting with NO.
- The NO ligand is neutral in its initial state and becomes +1 after the reaction.

2. **Charge transfer mechanism**:
- The NO ligand donates an electron to Fe2+, resulting in a change to Fe+.
- This is another example of ligand-to-metal charge transfer (LMCT), which gives rise to color (brown ring test).

### Step 4: Analyze CaCl2
1. **Nature of the compound**:
- Calcium chloride is an ionic compound and does not have d-orbitals available for charge transfer.
- There is no charge transfer mechanism involved.

### Conclusion
- The compounds that exhibit color due to charge transfer are:
- K2Cr2O7 (intense red color)
- KMnO4 (intense purple color)
- Fe(H2O)5NO(SO4) (color due to brown ring test)
- CaCl2 does not exhibit charge transfer.

### Final Answer
The compounds that give color due to charge transfer are:
- K2Cr2O7
- KMnO4
- Fe(H2O)5NO(SO4)