Correct statements about transition metals are that they:

Options

A. form complex
B. show variable oxidation states
C. show magnetic properties
D. do not from coloured compounds

Explanation

To determine which statements about transition metals are correct, we will analyze each statement one by one.

### Step 1: Analyze the statement "Transition metals form complexes."
- **Explanation**: Transition metals can form complexes due to the presence of vacant d orbitals. These vacant d orbitals allow transition metals to coordinate with ligands, which can donate electron pairs to the metal.
- **Conclusion**: This statement is **correct**.

### Step 2: Analyze the statement "Transition metals show variable oxidation states."
- **Explanation**: Transition metals exhibit variable oxidation states because they can lose different numbers of electrons from their d and s orbitals. For example, manganese (Mn) can have oxidation states of +2, +4, +6, and +7 due to the loss of electrons from its 3d and 4s orbitals.
- **Conclusion**: This statement is **correct**.

### Step 3: Analyze the statement "Transition metals show magnetic properties."
- **Explanation**: Transition metals can exhibit magnetic properties, particularly paramagnetism, due to the presence of unpaired electrons in their d orbitals. The unpaired electrons contribute to a net magnetic moment, making the metal paramagnetic.
- **Conclusion**: This statement is **correct**.

### Step 4: Analyze the statement "Transition metals do not form colored compounds."
- **Explanation**: This statement is incorrect. Transition metals often form colored compounds due to d-d transitions, where electrons in the d orbitals absorb specific wavelengths of light when they are excited to higher energy levels. The presence of unpaired electrons contributes to this phenomenon.
- **Conclusion**: This statement is **incorrect**.

### Final Summary:
- The correct statements about transition metals are:
1. They form complexes.
2. They show variable oxidation states.
3. They show magnetic properties.
- The incorrect statement is that they do not form colored compounds.