In a gaseous reaction of the type
`aA+ b B to c C + dD,`
(i) In a gaseous reaction of the type
(ii) a mole of A combines with b moles of B to give C and D
(iii) `(axxM_(A))` g of a combines with `(b xxM_(B))` g of B to give C and D
(iv) a molecules of A combines with b molecules of B to give C and D

Options

A. i, ii, iv
B. only iii
C. i, ii, iii and iv
D. ii and iv

Answer

To solve the question, we need to analyze the four statements provided regarding a gaseous reaction of the type \( aA + bB \rightarrow cC + dD \) and identify which statement is incorrect.

### Step 1: Analyze Each Statement

1. **Statement (i)**: "A mole of A combines with B moles of B to give C and D."
- This statement is correct. It follows the stoichiometric coefficients of the reaction.

2. **Statement (ii)**: "A liter of A combines with B liter of B to give C and D."
- This statement is also correct. In gaseous reactions, the volume of gases at the same temperature and pressure is proportional to the number of moles.

3. **Statement (iii)**: "(axxM_A) g of A combines with (b xxM_B) g of B to give C and D."
- This statement is incorrect. The correct formulation should specify the mass in terms of the number of moles multiplied by the molar mass. It should be \( (a \cdot M_A) \) g of A and \( (b \cdot M_B) \) g of B. The use of "axx" and "bxx" is ambiguous and misleading.

4. **Statement (iv)**: "a molecules of A combines with b molecules of B to give C and D."
- This statement is correct. It accurately represents the molecular interaction in the reaction.

### Conclusion
The incorrect statement is **Statement (iii)**.

### Final Answer
The incorrect statement is: **(iii) (axxM_A) g of A combines with (b xxM_B) g of B to give C and D.**

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