Which one of the following is a metal?

Options

A. graphite
B. iodine
C. phosphorus
D. magnesium

Explanation

To determine which of the following options is a metal, we will analyze each option based on the number of electrons in their outermost shell (valence shell). Metals typically have less than 4 electrons in their outermost shell.

### Step-by-Step Solution:

1. **Identify the Options**: The options given are graphite, iodine, phosphorus, and magnesium.

2. **Analyze Graphite**:
- Graphite is an allotrope of carbon.
- The atomic number of carbon is 6, which means it has 6 electrons.
- The electronic configuration is 2 in the first shell (K) and 4 in the second shell (L).
- The outermost shell (L shell) has 4 electrons.
- Since 4 electrons are present in the outermost shell, graphite is classified as a non-metal.

3. **Analyze Iodine**:
- Iodine is a halogen, belonging to group 17.
- The atomic number of iodine is 53.
- The electronic configuration shows that it has 7 electrons in its outermost shell (valence shell).
- Since 7 electrons are present in the outermost shell, iodine is classified as a non-metal.

4. **Analyze Phosphorus**:
- Phosphorus belongs to group 15.
- The atomic number of phosphorus is 15.
- The electronic configuration shows that it has 5 electrons in its outermost shell (valence shell).
- Since 5 electrons are present in the outermost shell, phosphorus is classified as a non-metal.

5. **Analyze Magnesium**:
- Magnesium is represented by the symbol Mg.
- The atomic number of magnesium is 12.
- The electronic configuration shows that it has 2 electrons in its outermost shell (valence shell).
- Since 2 electrons are present in the outermost shell, magnesium is classified as a metal.

6. **Conclusion**:
- Among the options, magnesium is the only element that qualifies as a metal because it has less than 4 electrons in its outermost shell.

### Final Answer:
**Magnesium is a metal.**

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