Metallic elements are described by their standard electrode potential, fusion enthalpy, atomic size, etc. The alkali metals are characerised by which of the following properties?

Options

A. High boiling point
B. High negative standard electrode potential
C. High density
D. Large atomic size

Explanation

To determine the properties that characterize alkali metals, we can analyze their common characteristics step by step.

### 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).

2. **Atomic Size**:
- Alkali metals have the largest atomic size in their respective periods. This is because they are the first element in their periods, leading to a lower effective nuclear charge (Z effective) experienced by the outermost electron. Hence, they have a larger atomic radius compared to other elements in the same period.

3. **Density**:
- Alkali metals have low density. This is due to their large atomic size and relatively low mass. The formula for density (density = mass/volume) indicates that with a large volume and low mass, the density will be low.

4. **Softness**:
- Alkali metals are soft and can be easily cut with a knife. This property is a result of their metallic structure and weak metallic bonding, which is influenced by their low ionization energy.

5. **Boiling Point**:
- Alkali metals have low boiling points compared to many other metals. This is again related to their weak metallic bonding.

6. **Ionization Energy and Electrode Potential**:
- Alkali metals have low ionization energies, which means they can easily lose their outermost electron. This results in a high negative standard electrode potential, indicating that they are highly reactive.

### Summary of Properties:
- **High Negative Standard Electrode Potential**: Correct
- **Low Density**: Correct
- **Large Atomic Size**: Correct
- **High Boiling Point**: Incorrect (they have low boiling points)

### Conclusion:
From the analysis, the properties that characterize alkali metals are:
- High negative standard electrode potential
- Large atomic size
- Low density
- They are soft metals

### Correct Options:
- High negative standard electrode potential (Correct)
- Large atomic size (Correct)
- Low density (Correct)
- High boiling point (Incorrect)

### Final Answer:
The alkali metals are characterized by:
- High negative standard electrode potential
- Large atomic size