Choose the incorrect statement.

Options

A. Chemical reactivity tends to be high in group 1 metals,lower in elementns in middle and increase to maximum in the group 17.
B. Halogens have very high negative electron gain enthalpy.
C. Noble gases have large positive electron gain enthalpy.
D. Decrease in electronegativities across a period is accompanied by an increase in non-metallic properties.

Explanation

To solve the question of identifying the incorrect statement among the given options, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Analyze Statement A:**
- **Statement:** Chemical reactivity tends to be high in group 1 metals, lower in the elements in the middle, and increases to a maximum in group 17.
- **Analysis:** Group 1 metals (alkali metals) are known for their high reactivity due to having one valence electron, which they lose easily. Group 17 elements (halogens) are also highly reactive as they need one electron to achieve a stable configuration. Therefore, this statement is **correct**.

2. **Analyze Statement B:**
- **Statement:** Halogens have very high negative electron gain enthalpy.
- **Analysis:** Halogens are indeed highly electronegative and have a strong tendency to gain electrons, resulting in a high negative electron gain enthalpy. Thus, this statement is also **correct**.

3. **Analyze Statement C:**
- **Statement:** Noble gases have large positive electron gain enthalpy.
- **Analysis:** Noble gases are stable and have a complete valence shell, meaning they do not readily gain electrons. When an electron is added, it requires a significant amount of energy, leading to a positive electron gain enthalpy. This statement is **correct**.

4. **Analyze Statement D:**
- **Statement:** Decrease in the electronegativities across a period is accompanied by an increase in nonmetallic character.
- **Analysis:** Electronegativity actually **increases** across a period from left to right, which correlates with an increase in nonmetallic character. Therefore, the first part of this statement is incorrect, making the entire statement **incorrect**.

### Conclusion:
The incorrect statement is **Option D**.

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