Which one of the following has the lowest m.p.?

Options

A. B
B. Al
C. Ga
D. Tl

Explanation

To determine which element among boron, aluminum, gallium, and thallium has the lowest melting point, we can follow these steps:

### Step 1: Understand the Elements
We need to analyze the elements given in the options:
- Boron (B)
- Aluminum (Al)
- Gallium (Ga)
- Thallium (Tl)

### Step 2: Check the Position in the Periodic Table
These elements belong to the same group (Group 13) of the periodic table. As we move down the group, the melting points generally decrease due to the increase in atomic size and the weakening of metallic bonds.

### Step 3: Compare Melting Points
Now, let’s look at the melting points of each element:
- Boron: It has a very high melting point due to its covalent network structure.
- Aluminum: It has a relatively high melting point, but lower than boron.
- Gallium: It has a lower melting point than aluminum and is unique because it can melt at temperatures slightly above room temperature (29.76 °C).
- Thallium: It has a melting point lower than that of aluminum but higher than gallium.

### Step 4: Identify the Lowest Melting Point
From the comparison:
- Boron has the highest melting point.
- Aluminum has a lower melting point than boron.
- Thallium has a lower melting point than aluminum.
- Gallium has the lowest melting point among these elements.

### Conclusion
Thus, the element with the lowest melting point is **Gallium (Ga)**.

### Final Answer
**Gallium (Ga)** has the lowest melting point among the given options.

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