Which of the following reaction involves the combination of two elements?

Options

A. `CaO + CO_(2) to CaCO_(3)`
B. `4Na + O_(3) to 2Na_(2) O`
C. `SO_(2) + 1/2 O_(2) to SO_(3)`
D. `NH_(3) + HC1 to NH_(4) C1`

Answer

To determine which of the following reactions involves the combination of two elements, we will analyze the options provided. A combination reaction occurs when two or more reactants combine to form a single product. Here’s how to approach the question step by step:

### Step-by-Step Solution:

1. **Understand the Definition of Elements and Compounds**:
- Elements are pure substances that consist of only one type of atom. Examples include oxygen (O), nitrogen (N), and neon (Ne).
- Compounds are substances formed when two or more different elements combine in a fixed ratio. For example, water (H2O) is a compound made of hydrogen and oxygen.

2. **Identify the Types of Reactions**:
- A combination reaction specifically involves the merging of two or more reactants to form one product.
- We need to look for reactions where both reactants are elements.

3. **Analyze Each Option**:
- **Option 1**: CAO + CO2 (Both are compounds)
- **Option 2**: Ne + O3 (Both are elements)
- **Option 3**: SO2 + O2 (O2 is an element, SO2 is a compound)
- **Option 4**: NH3 + Cl2 (Both are compounds)

4. **Determine the Correct Option**:
- From the analysis, only **Option 2 (Ne + O3)** involves the combination of two elements. Neon (Ne) is a noble gas, and ozone (O3) is a molecular form of oxygen.

5. **Conclusion**:
- The reaction that involves the combination of two elements is **Ne + O3**.