Which of the following is a decomposition reaction?

Options

A. `2KBr + C1_(2) to 2KC1 + Br_(2)`
B. `2Na + H_(2) O to 2NaOH + H_(2)`
C. `NH_(4) CNO to NH_(2) CONH_(2)`
D. ZnCO_(3) to ZnO + CO_(2)`

Answer

To determine which of the given reactions is a decomposition reaction, we first need to understand what a decomposition reaction is.

### Step-by-Step Solution:

1. **Definition of Decomposition Reaction**:
A decomposition reaction is a type of chemical reaction where a single compound breaks down into two or more simpler substances. The general form can be represented as:
\[ AB \rightarrow A + B \]
where \( AB \) is the compound that decomposes.

2. **Analyzing the Given Reactions**:
- **Reaction 1**: KBr + Cl2 → KCl + Br2
- This is a displacement reaction, where chlorine displaces bromine from potassium bromide.
- **Reaction 2**: NaH2 + H2O → NaOH + H2
- This is a reaction between sodium hydride and water, resulting in the formation of sodium hydroxide and hydrogen gas. It does not involve the breakdown of a single compound into simpler substances.
- **Reaction 3**: NH4CNO → NH2CONH2
- This reaction does not show the breakdown of a single compound into two or more products; hence it is not a decomposition reaction.
- **Reaction 4**: ZnC2 → (Assuming it decomposes into Zn + C2)
- If this reaction is indeed a decomposition reaction, it would fit the definition as it shows a compound breaking down into simpler substances.

3. **Conclusion**:
After analyzing all the reactions, if the last reaction (ZnC2) is confirmed to decompose into zinc and carbon, then it would be classified as a decomposition reaction.

### Final Answer:
The decomposition reaction among the options provided is the one that involves a compound breaking down into simpler substances, which is likely the last reaction (ZnC2 → Zn + C2).