Why does `H^(+)` ion always get associated with atoms or molecules ?

Options

A. Ionisation enthalpy of hydrogen resembles that of alkali metals.
B. Its reactivity is similar to halogens.
C. It resembles both alkali metals and halogens.
D. Loss of an electron from hydrogen atom results in a nucleus of very small size as compared to other atoms or ions. Due to small size it cannot exist free.

Explanation

### Step-by-Step Solution:

1. **Understanding the Hydrogen Ion (H⁺)**:
- The hydrogen ion (H⁺) is formed when a hydrogen atom loses its single electron. This results in a positively charged ion.

2. **Characteristics of H⁺**:
- The H⁺ ion is essentially just a proton, as it has no electrons. This means it has a very small size compared to other ions and atoms.

3. **Why H⁺ Cannot Exist Freely**:
- Due to its small size, the H⁺ ion has a very high charge density. This high charge density leads to a strong attraction to nearby electrons from other atoms or molecules.
- As a result, H⁺ ions tend to associate with other atoms or molecules to stabilize themselves. They cannot exist freely in a solution or in the gaseous state.

4. **Comparison with Other Ions**:
- Unlike larger ions, which can exist independently due to their size and electron configuration, H⁺ lacks the necessary electron cloud to shield its positive charge. Therefore, it readily associates with other species.

5. **Conclusion**:
- The primary reason that H⁺ ions always associate with atoms or molecules is their small size, which leads to a strong attraction to other atoms or molecules, preventing them from existing freely.