Hardness of transition metals is due to

Options

A. Large atomic size
B. Metallic bonding
C. Ionic bond
D. High ionization energy

Answer

To determine the reason for the hardness of transition metals, we can analyze the options provided and the characteristics of transition metals.

### Step-by-Step Solution:

1. **Understanding Transition Metals**: Transition metals are elements found in the d-block of the periodic table. They are characterized by the presence of d-electrons, which can be either paired or unpaired.

2. **Analyzing the Options**:
- **Option 1: Due to the large atomic size**: While atomic size can influence properties, it is not the primary reason for the hardness of transition metals.
- **Option 2: Metallic bonding**: Transition metals exhibit strong metallic bonding due to the presence of unpaired d-electrons that can overlap and form bonds with neighboring atoms.
- **Option 3: Ionic bond**: Transition metals typically do not form ionic bonds in a way that contributes to their hardness.
- **Option 4: High ionization energy**: While transition metals can have relatively high ionization energies, this is not the main factor contributing to their hardness.

3. **Role of Unpaired d-Electrons**: The unpaired d-electrons in transition metals allow for the formation of covalent bonds through overlap. The more unpaired d-electrons present, the stronger the covalent bonds formed, which directly contributes to the hardness of the metal.

4. **Conclusion**: The hardness of transition metals is primarily due to the strong metallic bonding, which arises from the overlapping of unpaired d-electrons between different metal atoms. Therefore, the correct answer is **Option 2: Metallic bonding**.

### Final Answer:
The hardness of transition metals is due to **metallic bonding**.

---