Choose total number of correct reaction.
(i) When `CuSO_(4)` solution reacts with `NH_(3)`, complex is formed.
(ii) When `CuSO_(4)` solution react withh `PH_(3)`, complex is formed.
(iii) `C_(12)H_(22)O_(11) overset("conc. "H_(2)SO_(4)) to 2C+11H_(2)O`
(iv) `underset(("excess"))(NH_(3))+Cl_(2) overset(Delta) to NH_(4)Cl+N_(2)`

Explanation

To determine the total number of correct reactions from the given options, we will analyze each reaction step by step.

### Step 1: Analyze Reaction (i)
**Reaction:** When `CuSO4` solution reacts with `NH3`, a complex is formed.

**Explanation:**
When copper sulfate (CuSO4) reacts with ammonia (NH3), it forms a complex ion, specifically [Cu(NH3)4]²⁺, which is a blue-colored complex. This reaction is indeed correct.

**Conclusion:** Reaction (i) is correct.

### Step 2: Analyze Reaction (ii)
**Reaction:** When `CuSO4` solution reacts with `PH3`, a complex is formed.

**Explanation:**
When copper sulfate reacts with phosphine (PH3), it does not form a complex. Instead, it forms copper phosphide (Cu3P2), which is a black solid. Therefore, no complex is formed in this reaction.

**Conclusion:** Reaction (ii) is incorrect.

### Step 3: Analyze Reaction (iii)
**Reaction:** `C12H22O11` (sucrose) reacts with concentrated `H2SO4` to form `2C + 11H2O`.

**Explanation:**
When sucrose (C12H22O11) is treated with concentrated sulfuric acid (H2SO4), it undergoes dehydration, leading to the formation of carbon (C) and water (H2O). This reaction is a well-known dehydration reaction of sugar.

**Conclusion:** Reaction (iii) is correct.

### Step 4: Analyze Reaction (iv)
**Reaction:** Excess `NH3` + `Cl2` (heat) → `NH4Cl` + `N2`.

**Explanation:**
When ammonia (NH3) reacts with chlorine (Cl2) under heat, it can produce nitrogen gas (N2) and ammonium chloride (NH4Cl). The reaction can proceed in such a way that if ammonia is in excess, it can lead to the formation of these products.

**Conclusion:** Reaction (iv) is correct.

### Final Conclusion
After analyzing all four reactions, we find that:
- Reaction (i) is correct.
- Reaction (ii) is incorrect.
- Reaction (iii) is correct.
- Reaction (iv) is correct.

**Total Number of Correct Reactions:** 3 (i, iii, and iv)

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