Transition metals usually from coloured complexes and d-d transitions `(t_(2g)hArre_(g))` are responsible for colour as the energy difference between `t_(2g)` and `e_(g)` lies in visible region. But all the coloured ions are not dut to d-d transition but charge transfer bands also play important roles. Charge transfer bands may be of two types.
(i) ligand to metal (CTLM)`" "(ii)` metal to ligand (CTML).
Charge transfer transition always produces intense colour as compared to d-d transition.
Select the incorrect statement `:`

Options

A. d-block metal ions are usually coloured.
B. colour of the most of d-block metal ions is enerally due to d-d transiton.
C. All the complexes of `Cu^(+)` are colourless on account of diamagnetic nature i.e., `d^(10)` configuration
D. `CrO_(3)` is bright orange due to CTLM.

Answer

To solve the question regarding the statements about transition metals and their color properties, let's analyze each statement step by step.

### Step-by-Step Solution:

1. **Understanding d-d Transitions:**
- Transition metals are known to form colored complexes due to d-d transitions. The d-orbitals split into two energy levels: \(t_{2g}\) and \(e_g\). The energy difference between these levels falls within the visible spectrum, allowing for color to be observed when electrons transition between these levels.

**Hint:** Recall that d-d transitions involve the movement of electrons within the d-orbitals of the metal ions.

2. **Color of Transition Metals:**
- It is true that most colored transition metal complexes are due to d-d transitions. However, this is not the sole reason for color. Charge transfer transitions can also contribute to the color observed in these complexes.

**Hint:** Remember that while d-d transitions are common, charge transfer transitions can also result in color, especially in certain configurations.

3. **Types of Charge Transfer:**
- Charge transfer bands can be classified into two types:
- Ligand to Metal (CTLM)
- Metal to Ligand (CTML)
- Charge transfer transitions are generally more intense than d-d transitions, leading to more vivid colors.

**Hint:** Differentiate between the two types of charge transfer transitions and their implications on color intensity.

4. **Evaluating the Statements:**
- **Statement A:** "D-block metal ions are usually colored."
- This is correct because most d-block metal ions do exhibit color due to d-d transitions.

- **Statement B:** "Color of most d-block metal ions is entirely due to d-d transitions."
- This is incorrect. While d-d transitions contribute to color, they are not the only source, especially for d0, d5, and d10 configurations where charge transfer plays a significant role.

- **Statement C:** "All complexes of Cu⁺ are colorless on account of diamagnetic nature."
- This is correct. Cu⁺ has a d10 configuration, which does not allow for d-d transitions, leading to colorlessness.

- **Statement D:** "CrO₃ is bright orange due to CTLM."
- This is correct. In CrO₃, the charge transfer from ligand to metal contributes to its bright orange color.

5. **Conclusion:**
- The incorrect statement is **Statement B**, which claims that the color of most d-block metal ions is entirely due to d-d transitions. This is not true as charge transfer can also contribute significantly to the color observed.

### Final Answer:
The incorrect statement is **B**: "Color of most d-block metal ions is entirely due to d-d transitions."