Which of the following are combination reactions?
` (i) 2KClO_(3)overset("Heat")to2KCl+3O_(2)`
`(ii) MgO+H_(2)OtoMg(OH)_(2)`
`(iii) 4Al+3O_(2)to 2Al_(2)O_(3)`
`(iv) Zn+FeSO_(4)to ZnSO_(4)+Fe`

Options

A. Both (i) and (iii)
B. Both (iii) and(iv)
C. Both (ii) and (iv)
D. Both (ii) and (iii)

Explanation

To determine which of the given reactions are combination reactions, we first need to understand what a combination reaction is. A combination reaction occurs when two or more reactants combine to form a single product.

Now, let's analyze each of the provided reactions step by step:

### Step 1: Analyze Reaction (i)
**Reaction:** \( 2KClO_3 \overset{\text{Heat}}{\rightarrow} 2KCl + 3O_2 \)

- **Type:** This reaction involves the decomposition of potassium chlorate (\(KClO_3\)) into potassium chloride (\(KCl\)) and oxygen gas (\(O_2\)).
- **Conclusion:** This is a **decomposition reaction**, not a combination reaction.

### Step 2: Analyze Reaction (ii)
**Reaction:** \( MgO + H_2O \rightarrow Mg(OH)_2 \)

- **Type:** Here, magnesium oxide (\(MgO\)) combines with water (\(H_2O\)) to form magnesium hydroxide (\(Mg(OH)_2\)).
- **Conclusion:** This is a **combination reaction** because two reactants combine to form a single product.

### Step 3: Analyze Reaction (iii)
**Reaction:** \( 4Al + 3O_2 \rightarrow 2Al_2O_3 \)

- **Type:** In this reaction, aluminum (\(Al\)) reacts with oxygen (\(O_2\)) to form aluminum oxide (\(Al_2O_3\)).
- **Conclusion:** This is also a **combination reaction** as two reactants combine to form one product.

### Step 4: Analyze Reaction (iv)
**Reaction:** \( Zn + FeSO_4 \rightarrow ZnSO_4 + Fe \)

- **Type:** This reaction involves zinc (\(Zn\)) displacing iron (\(Fe\)) from iron(II) sulfate (\(FeSO_4\)) to form zinc sulfate (\(ZnSO_4\)) and iron.
- **Conclusion:** This is a **displacement reaction**, not a combination reaction.

### Final Conclusion:
From the analysis, we find that:
- Reaction (ii) and Reaction (iii) are combination reactions.
- Reaction (i) is a decomposition reaction.
- Reaction (iv) is a displacement reaction.

Thus, the combination reactions are **(ii) and (iii)**.

### Answer:
The combination reactions are (ii) and (iii).

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