Which statements are incorrect about transition elements ?

Options

A. They show variable valency
B. They readily form complex compounds
C. All their ions are colourless
D. Their ions contain partially filled d - orbital

Answer

To determine which statements are incorrect about transition elements, let's analyze each of the provided options step by step:

1. **They show variable valency**:
- Transition elements are known for exhibiting variable oxidation states due to the involvement of d-electrons in bonding. This statement is **correct**.

2. **They readily form complex compounds**:
- Transition metals can form complex ions with ligands due to their ability to accommodate lone pairs of electrons. This statement is also **correct**.

3. **All their ions are colorless**:
- This statement is **incorrect**. Many transition metal ions are colored due to d-d transitions of electrons in partially filled d-orbitals. For example, copper(II) ions are blue, and iron(III) ions are yellow. Therefore, this statement does not hold true for transition elements.

4. **Their ions contain partially filled d-orbital**:
- Transition metals have partially filled d-orbitals, which is a defining characteristic of these elements. This statement is **correct**.

Based on the analysis, the only incorrect statement about transition elements is: **"All their ions are colorless."**

### Summary of the Solution:
- **Correct Statements**:
1. They show variable valency.
2. They readily form complex compounds.
3. Their ions contain partially filled d-orbitals.
- **Incorrect Statement**:
- All their ions are colorless.