Which gas is most soluble in water?

Options

A. He
B. `H_2`
C. `NH_3`
D. `CO_2`

Answer

To determine which gas is most soluble in water from the given options (Helium, Hydrogen, Ammonia, CO2), we can analyze the properties of each gas in relation to water's characteristics.

### Step-by-Step Solution:

1. **Understanding Polarity of Water:**
- Water (H2O) is a polar molecule due to the significant electronegativity difference between oxygen and hydrogen. This polarity allows water to dissolve other polar substances effectively.

**Hint:** Remember that "like dissolves like" means polar solvents dissolve polar solutes.

2. **Analyzing Each Gas:**
- **Helium (He):**
- Helium is a noble gas and is non-polar. It does not interact favorably with water molecules, leading to very low solubility.
- **Hydrogen (H2):**
- Hydrogen gas is also non-polar. Since it does not have polar characteristics, it is not soluble in water.
- **Ammonia (NH3):**
- Ammonia is a polar molecule. The nitrogen atom in ammonia can form hydrogen bonds with water molecules, enhancing its solubility in water.
- **Carbon Dioxide (CO2):**
- Carbon dioxide is a polar molecule and can dissolve in water, but it does not form hydrogen bonds as effectively as ammonia.

3. **Comparing Solubility:**
- Among the gases listed, ammonia has the highest solubility in water due to its ability to form hydrogen bonds with water molecules, while helium and hydrogen have very low solubility due to their non-polar nature. Carbon dioxide is soluble but not as much as ammonia.

4. **Conclusion:**
- Therefore, the gas that is most soluble in water from the given options is **Ammonia (NH3)**.

**Final Answer:** Ammonia (NH3) is the most soluble gas in water.