Which of the following are the correct reasons for anomlaous behaviour of lithium?

Options

A. Exceptionally small size of its atom
B. Its high polarising power
C. It has high degree of hydration
D. Exceptionally low ionisation enthalpy

Explanation

To determine the correct reasons for the anomalous behavior of lithium, we can analyze the properties of lithium compared to other alkali metals. Here’s the step-by-step solution:

### Step 1: Understand the Size of Lithium
- Lithium (Li) has a very small atomic and ionic size compared to other alkali metals. This small size is a key factor in its unique properties.

**Hint:** Consider how size affects the behavior of ions in chemical reactions.

### Step 2: High Polarizing Power
- Due to its small size, the Li+ ion has a high polarizing power. This means it can distort the electron cloud of nearby anions more effectively than larger alkali metal ions.

**Hint:** Think about how the ability to distort electron clouds influences chemical bonding and properties.

### Step 3: Anomalous Properties of Lithium
- Lithium exhibits several anomalous properties compared to other alkali metals:
1. **Higher Melting and Boiling Points**: Lithium has higher melting and boiling points than other alkali metals.
2. **Hardness**: Lithium is harder than other alkali metals.
3. **Decomposition of Lithium Nitrate**: Lithium nitrate decomposes to form lithium oxide, while other alkali metal nitrates decompose to form nitrites.

**Hint:** Identify how these properties differ from those of other alkali metals and relate them back to lithium's unique characteristics.

### Step 4: Evaluate the Given Options
- Now, we can evaluate the options provided:
1. **Exceptionally Small Size**: Correct, as it contributes to high polarizing power.
2. **High Polarizing Power**: Correct, as it leads to the anomalous behavior.
3. **High Degree of Hydration**: Incorrect, as this is not a reason for the anomalous behavior.
4. **Exceptionally Low Ionization Enthalpy**: Incorrect, because lithium has a relatively high ionization enthalpy.

**Hint:** Cross-check each option against the properties and reasons discussed.

### Conclusion
- The correct reasons for the anomalous behavior of lithium are:
- Exceptionally small size (Option 1)
- High polarizing power (Option 2)

### Final Answer
- The correct options are 1 and 2.

---