Select the incorrect statement(s):

Options

A. `Cs^(+)` is more hydrated than the other alkali metal ions
B. Among the alkali metals Li, Na, K and Rb, lithium has the highest melting point
C. Ionic mobility of `Li^(+)` is maximum among alkali metal cations
D. Ionisation potential of `Li` is lower than that of Na

Answer

To solve the question of selecting the incorrect statements regarding alkali metals, we will analyze each statement one by one.

### Step 1: Analyze the first statement
**Statement:** Cesium ion is more hydrated than other alkali metal ions.

**Analysis:** Hydration energy is inversely proportional to the size of the ion. Cesium ion (Cs⁺) is the largest among alkali metal ions, which means it has the lowest hydration energy. Therefore, this statement is incorrect.

### Step 2: Analyze the second statement
**Statement:** Among alkali metals, lithium has the highest melting point.

**Analysis:** The melting points of alkali metals generally decrease down the group. Lithium has a melting point of 180.5 °C, while sodium (Na) has a melting point of 97.8 °C, potassium (K) has a melting point of 63.5 °C, and rubidium (Rb) has a melting point of 39.3 °C. However, lithium does not have the highest melting point; rather, it is cesium that has the lowest melting point. Therefore, this statement is also incorrect.

### Step 3: Analyze the third statement
**Statement:** Ionic mobility of lithium ion (Li⁺) is maximum among alkali metals.

**Analysis:** Lithium ion is small in size, which allows it to have high ionic mobility in solution compared to other alkali metal ions. Thus, this statement is correct.

### Step 4: Analyze the fourth statement
**Statement:** Ionization potential of lithium is lower than that of sodium.

**Analysis:** Ionization energy generally increases as we move up the group in the periodic table. Since lithium is smaller than sodium, it has a higher ionization energy. Therefore, this statement is incorrect.

### Conclusion
The incorrect statements are:
- Statement 1: Cesium ion is more hydrated than other alkali metal ions (Incorrect)
- Statement 2: Among alkali metals, lithium has the highest melting point (Incorrect)
- Statement 4: Ionization potential of lithium is lower than that of sodium (Incorrect)

Thus, the answer to the question is that statements 1, 2, and 4 are incorrect.

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