Which relations between equivalent weight (E) and Molecular weight (M) of reactant are correct for the given change?

Options

A. `FeCl_(2)` into `Fe(OH)_(2):E=M/2`
B. `Fe_(2)(SO_(4))_(3)` into `Fe^(+2),E=M/2`
C. `FeSO_(4)` into `Fe_(2)(SO_(4))_(3),E=M/2`
D. `K_(2)MnO_(4)` into `KMnO_(4):E=M/2`

Answer

To solve the question regarding the relationship between equivalent weight (E) and molecular weight (M) of reactants during a chemical change, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding Equivalent Weight (E) and Molecular Weight (M)**:
- The equivalent weight (E) of a substance is defined as the mass of the substance that combines with or displaces 1 mole of hydrogen or 1/2 mole of oxygen in a reaction.
- The molecular weight (M) is the mass of one mole of a substance.

2. **Analyzing Option 1: FeCl2 to Fe(OH)2**:
- In FeCl2, the oxidation state of Fe is +2.
- In Fe(OH)2, the oxidation state of Fe remains +2.
- Since there is no change in oxidation state, the equivalent weight does not change.
- Therefore, the relation is E = M (but this option is stated as incorrect).

**Hint**: Check for changes in oxidation states to determine if equivalent weights change.

3. **Analyzing Option 2: Fe2(SO4)3 to Fe2+**:
- In Fe2(SO4)3, the oxidation state of Fe is +3.
- In Fe2+, the oxidation state of Fe is +2.
- The change in oxidation state is +1 for each Fe atom, and since there are 2 Fe atoms, the total change is 2.
- Thus, the equivalent weight is given by E = M/2.

**Hint**: Calculate the change in oxidation state to find the equivalent weight.

4. **Analyzing Option 3: FeSO4 to Fe2(SO4)2**:
- In FeSO4, the oxidation state of Fe is +2.
- In Fe2(SO4)2, the oxidation state of Fe remains +2.
- There is no change in oxidation state, so the equivalent weight does not change.
- Therefore, this option is also incorrect.

**Hint**: Compare oxidation states before and after the reaction to see if they remain the same.

5. **Analyzing Option 4: K2MnO4 to KMnO4**:
- In K2MnO4, the oxidation state of Mn is +6.
- In KMnO4, the oxidation state of Mn is +7.
- The change in oxidation state is +1.
- Therefore, the equivalent weight is given by E = M/1.

**Hint**: Identify the change in oxidation state to determine the equivalent weight.

6. **Conclusion**:
- From the analysis, we find that:
- Option 1 is incorrect (E = M).
- Option 2 is correct (E = M/2).
- Option 3 is incorrect (E = M).
- Option 4 is incorrect (E = M/1).
- The only correct relation is from Option 2: E = M/2.

### Final Answer:
The correct relation between equivalent weight (E) and molecular weight (M) for the given change is from **Option 2: E = M/2**.