The alkali metals have low melting point. Which of the following alkali metal is expected to melt if the room temperature rises to `30^(@)C` ?

Options

A. `Na`
B. K
C. `Rb`
D. `Cs`

Explanation

To determine which alkali metal is expected to melt if the room temperature rises to 30°C, we need to analyze the melting points of the alkali metals and understand the trend in their melting points.

### Step-by-Step Solution:

1. **Understanding Melting Points of Alkali Metals**:
- Alkali metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).
- These metals have relatively low melting points compared to other metals.

2. **List of Melting Points**:
- Lithium (Li): 180.5°C
- Sodium (Na): 97.8°C
- Potassium (K): 63.5°C
- Rubidium (Rb): 39.3°C
- Cesium (Cs): 28.5°C

3. **Identify the Melting Point Below Room Temperature**:
- Room temperature is given as 30°C.
- Among the listed melting points, cesium (Cs) has a melting point of 28.5°C, which is below 30°C.

4. **Conclusion**:
- Since cesium has a melting point that is just below room temperature, it is expected to melt if the temperature rises to 30°C.

Thus, the alkali metal that is expected to melt at a room temperature of 30°C is **cesium (Cs)**.