The reaction which proceeds in the backward direction is

Options

A. (a) `Fe_(3)O_(4)+6HClhArr2FeCl_(3)+3H_(2)O`
B. (b) `NH_(3)+H_(2)O+NaClhArrNH_(4)Cl+NaOH`
C. (c) `SnCl_(4)+Hg_(2)Cl_(2)hArrSnCl_(2)+2HgCl_(2)`
D. (d) `2CuI+I_(2)+4K^(o+)hArr2Cu^(2+)+4KI`

Answer

To determine which reactions proceed in the backward direction, we will analyze each option provided in the question step by step.

### Step 1: Analyze Option A
**Reaction:** Fe3O4 + 6 HCl ⇌ 2 FeCl3 + 3 H2O

- This reaction is an acid-base neutralization reaction where HCl (an acid) reacts with Fe3O4 (a base).
- In acid-base reactions, the tendency is for the reaction to proceed forward to form the products.
- **Conclusion:** This reaction proceeds in the forward direction.

### Step 2: Analyze Option B
**Reaction:** NH3 + H2O + NaCl ⇌ NH4Cl + NaOH

- Here, NaOH is a strong base that reacts with the salt of a strong acid (NH4Cl).
- The presence of a strong base suggests that the equilibrium will shift to favor the reactants, as the strong base will drive the reaction backward.
- **Conclusion:** This reaction proceeds in the backward direction.

### Step 3: Analyze Option C
**Reaction:** SnCl4 + Hg2Cl2 ⇌ SnCl2 + HgCl2

- In this reaction, Sn4+ and Hg2+ are more stable than Sn2+ and Hg+.
- Since the products (SnCl2 and HgCl2) are in a lower oxidation state and less stable, the equilibrium will shift toward the reactants.
- **Conclusion:** This reaction proceeds in the backward direction.

### Step 4: Analyze Option D
**Reaction:** 2 CuI + I2 + 4 K ⇌ 2 Cu2+ + 4 KI

- For copper, Cu+ has a fully filled d-orbital configuration (3d10), while Cu2+ has a partially filled configuration (3d9).
- The stability of Cu+ compared to Cu2+ indicates that the reaction will favor the reactants, thus shifting the equilibrium backward.
- **Conclusion:** This reaction proceeds in the backward direction.

### Final Conclusion
From the analysis:
- **Option A** proceeds in the forward direction.
- **Options B, C, and D** proceed in the backward direction.

Therefore, the correct answer to the question "The reaction which proceeds in the backward direction is" includes options B, C, and D.

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