Which is/are INCORRECT statement ?

Options

A. Equivalent mass of `H_(2)PO_(3)^(-)` is 40.5.
B. Eq. mass of `H_(2)PO_(4)^(-)` may be equal to molar mass or less than molar mass because it depends on the reaction.
C. `KMnO_(4)` has maximum eq. mass in acidic medium.
D. Oxidation state of H in `MgH_(2)` is greater than in `H_(2)O_(2)`.

Answer

To determine which statements are incorrect, we will analyze each statement one by one based on the principles of stoichiometry and oxidation states.

### Step-by-Step Solution

1. **Evaluate Statement A**: "Equivalent mass of H2PO3- is 40.5."
- To find the equivalent mass, we use the formula:
\[ \text{Equivalent mass} = \frac{\text{Molar mass}}{n\text{-factor}} \]
- The n-factor depends on the reaction context. Since no specific reaction is provided, we cannot definitively state that the equivalent mass is 40.5. Therefore, this statement is **incorrect**.

2. **Evaluate Statement B**: "Equivalent mass of H2PO4- may be equal to molar mass or less than molar mass because it depends on the reaction."
- The n-factor for H2PO4- can vary based on the reaction. If the n-factor is 1, the equivalent mass equals the molar mass. If the n-factor is greater than 1, the equivalent mass will be less than the molar mass. This statement is **correct**.

3. **Evaluate Statement C**: "KMnO4 has maximum equivalent mass in acidic medium."
- In acidic medium, KMnO4 (permanganate ion) reduces from MnO4- (oxidation state +7) to Mn2+ (oxidation state +2), which involves a change of 5 electrons (n-factor = 5). Thus, the equivalent mass is:
\[ \text{Equivalent mass} = \frac{\text{Molar mass}}{5} \]
- In basic medium, it reduces to MnO4+ (oxidation state +4), involving a change of 3 electrons (n-factor = 3). Thus, the equivalent mass is:
\[ \text{Equivalent mass} = \frac{\text{Molar mass}}{3} \]
- Since \(\frac{\text{Molar mass}}{3} > \frac{\text{Molar mass}}{5}\), the equivalent mass is greater in basic medium than in acidic medium. Therefore, this statement is **incorrect**.

4. **Evaluate Statement D**: "Oxidation state of hydrogen in MgH2 is greater than in H2O2."
- In MgH2, hydrogen has an oxidation state of -1 (as it is bonded to a metal). In H2O2, hydrogen has an oxidation state of +1 (as it is bonded to nonmetals). Since -1 is less than +1, this statement is **incorrect**.

### Conclusion
The incorrect statements are:
- Statement A: "Equivalent mass of H2PO3- is 40.5."
- Statement C: "KMnO4 has maximum equivalent mass in acidic medium."
- Statement D: "Oxidation state of hydrogen in MgH2 is greater than in H2O2."

Thus, the incorrect statements are A, C, and D.

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