Elements in the first column of the periodic table are called alkali metals. These metals have:

Options

A. A single valency electron
B. One electron less than an inert gas configuration
C. High melting points
D. High ionisation potentals

Answer

To answer the question regarding the properties of alkali metals, we will analyze each option provided.

### Step-by-Step Solution:

1. **Understanding Alkali Metals**:
- Alkali metals are located in Group 1 of the periodic table. They include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).
- These metals are known for their reactivity and the formation of strong bases (alkalis) when they react with water.

2. **Analyzing Each Option**:
- **Option A: A single valence electron**:
- Alkali metals have one electron in their outermost shell (s subshell). This makes this statement true.
- **Option B: One electron less than an inert gas configuration**:
- Alkali metals actually have one more electron than the nearest noble gas configuration. Therefore, this statement is false.
- **Option C: High melting points**:
- Alkali metals are characterized by low melting points compared to other metals. Thus, this statement is also false.
- **Option D: High ionization potential**:
- Alkali metals have the lowest ionization potential in their respective periods, making this statement false as well.

3. **Conclusion**:
- The only correct statement about alkali metals is that they have a single valence electron (Option A).

### Final Answer:
The correct answer is **A: A single valence electron**.