The characteristic not related to alkali metal is

Options

A. Their ions are isoelectronic with noble gases
B. Low melting point
C. Low electronegativity
D. High ionization energy

Explanation

To determine the characteristic that is not related to alkali metals, we need to analyze the given options one by one. Alkali metals are known for certain properties, and we will identify which of the options does not align with these properties.

### Step-by-Step Solution:

1. **Understanding Alkali Metals:**
Alkali metals are found 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 characterized by their tendency to lose one electron to form cations with a +1 charge.

2. **Analyzing the Options:**
- **Option 1: "Their ions are isoelectronic with noble gases."**
- Alkali metals lose one electron to form cations (e.g., Li⁺, Na⁺). These cations have the same electron configuration as the nearest noble gas (e.g., Li⁺ is isoelectronic with He, Na⁺ is isoelectronic with Ne). This statement is true for alkali metals.

- **Option 2: "Low melting point of alkali metals in their periods."**
- Alkali metals generally have low melting points compared to other metals in the same period. This statement is also true.

- **Option 3: "Low electronegativity."**
- Alkali metals have low electronegativity values, which increase as you move from left to right across a period. This statement is true.

- **Option 4: "High ionization energy."**
- Alkali metals have low ionization energies because they easily lose their outermost electron. This statement is false, as alkali metals are characterized by low ionization energies.

3. **Conclusion:**
The characteristic that is not related to alkali metals is **"High ionization energy."**

### Final Answer:
The characteristic not related to alkali metals is **"High ionization energy."**