Which of the following statement is not correct about group-16?

Options

A. `O_(2)` is a diatomic molecule
B. Hydrogen bonding is present in `H_(2)O`
C. Sulphur shows covalency of 3
D. All elements react with halogens.

Explanation

To determine which statement is not correct about Group 16 elements, we need to analyze the characteristics and properties of these elements. Group 16 elements, also known as the chalcogens, include oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and polonium (Po).

### Step-by-Step Solution:

1. **Identify the Elements in Group 16**:
- The elements in Group 16 are: Oxygen (O), Sulfur (S), Selenium (Se), Tellurium (Te), and Polonium (Po).

2. **Check the Valence Electrons**:
- Each of these elements has six valence electrons. This is important for understanding their bonding behavior.

3. **Examine the Diatomic Nature of Oxygen**:
- Oxygen exists as a diatomic molecule (O2) in its gaseous form, which is a true statement.

4. **Consider Hydrogen Bonding in Water**:
- Water (H2O) contains hydrogen bonds due to the electronegativity of oxygen. This statement is also true.

5. **Evaluate Covalency**:
- The statement regarding the covalency of 3 is incorrect. The maximum covalency of Group 16 elements can be 6, as they can form up to six bonds (e.g., in compounds like OF2).

6. **Check Reactivity with Halogens**:
- It is true that all Group 16 elements can react with halogens. For example, oxygen can react with fluorine to form OF2.

7. **Conclusion**:
- The statement that mentions "covalency of 3" is the one that is not correct about Group 16 elements.

### Final Answer:
The statement that is not correct about Group 16 is: "The covalency of Group 16 elements is 3."