Which is dibasic?

Options

A. Orthophosphoric acid
B. Pyrophosphoric acid
C. Orthophosphorus acid
D. Hypophosphorus acid

Answer

To determine which of the given acids is dibasic, we need to analyze the basicity of each acid based on their structures. A dibasic acid can donate two protons (H⁺ ions) when dissolved in water. Let's go through the options step by step.

### Step 1: Analyze Orthophosphoric Acid (H₃PO₄)
- **Structure**: The structure of orthophosphoric acid can be represented as:
```
O
||
HO - P - OH
|
OH
```
- **Basicity**: Orthophosphoric acid has three hydroxyl (OH) groups, which means it can donate three protons. Therefore, it is **tribasic**.

### Step 2: Analyze Pyrophosphoric Acid (H₄P₂O₇)
- **Structure**: The structure of pyrophosphoric acid can be represented as:
```
O O
|| ||
HO - P - O - P - OH
| |
OH OH
```
- **Basicity**: Pyrophosphoric acid has four hydroxyl (OH) groups, which means it can donate four protons. Therefore, it is **tetra-basic**.

### Step 3: Analyze Orthophosphorus Acid (H₃PO₃)
- **Structure**: The structure of orthophosphorus acid can be represented as:
```
O
||
HO - P - OH
|
H
```
- **Basicity**: Orthophosphorus acid has two hydroxyl (OH) groups and one hydrogen that is not part of an OH group. Therefore, it can donate two protons. Thus, it is **dibasic**.

### Step 4: Analyze Hypophosphorus Acid (H₃PO₂)
- **Structure**: The structure of hypophosphorus acid can be represented as:
```
O
||
HO - P - H
|
H
```
- **Basicity**: Hypophosphorus acid has only one hydroxyl (OH) group, which means it can donate only one proton. Therefore, it is **monobasic**.

### Conclusion
Based on the analysis:
- Orthophosphoric acid is tribasic.
- Pyrophosphoric acid is tetra-basic.
- Orthophosphorus acid is dibasic.
- Hypophosphorus acid is monobasic.

Thus, the dibasic acid among the given options is **orthophosphorus acid (H₃PO₃)**.