If the molecular weight of `H_(3)PO_(3)` is M, its equivalent weight will be .

Options

A. M
B. M/2
C. M/3
D. 2M

Explanation

To find the equivalent weight of \( H_3PO_3 \) given that its molecular weight is \( M \), we can follow these steps:

### Step 1: Understand the concept of equivalent weight
The equivalent weight of a substance is calculated using the formula:
\[ \text{Equivalent Weight} = \frac{\text{Molecular Weight}}{N} \]
where \( N \) is the number of equivalents, which can be defined based on the number of replaceable hydrogen ions (H\(^+\)) in acids.

### Step 2: Determine the structure of \( H_3PO_3 \)
The structure of \( H_3PO_3 \) (phosphorous acid) can be represented as:
- One phosphorus atom (P) bonded to three oxygen atoms (O).
- Two of these oxygen atoms are bonded to hydrogen atoms (OH groups), and one oxygen is double-bonded to phosphorus.

### Step 3: Identify the replaceable hydrogen ions
In \( H_3PO_3 \):
- There are two hydroxyl (OH) groups, which means there are two replaceable hydrogen ions (H\(^+\)).
- Therefore, the number of replaceable H\(^+\) ions, which is the N factor, is 2.

### Step 4: Calculate the equivalent weight
Using the formula for equivalent weight:
\[ \text{Equivalent Weight} = \frac{M}{N} \]
Substituting \( N = 2 \):
\[ \text{Equivalent Weight} = \frac{M}{2} \]

### Conclusion
Thus, the equivalent weight of \( H_3PO_3 \) is:
\[ \frac{M}{2} \]