A vessel of 120 mL capacity contains a certain amount of gas at 1.2 bar pressure and `35^(@)C`. The gas is transferred to another vessel of volume 180 mL at `35^(@)C`. What would be its pressure?

Explanation

To solve the problem, we will use Boyle's Law, which states that for a given mass of gas at constant temperature, the product of pressure and volume is constant. This can be expressed mathematically as:

\[ P_1 V_1 = P_2 V_2 \]

### Step-by-step Solution:

1. **Identify the given values**:
- Initial pressure, \( P_1 = 1.2 \, \text{bar} \)
- Initial volume, \( V_1 = 120 \, \text{mL} \)
- Final volume, \( V_2 = 180 \, \text{mL} \)
- Final pressure, \( P_2 \) (to be calculated)

2. **Write down Boyle's Law**:
\[ P_1 V_1 = P_2 V_2 \]

3. **Substitute the known values into the equation**:
\[ 1.2 \, \text{bar} \times 120 \, \text{mL} = P_2 \times 180 \, \text{mL} \]

4. **Calculate the left side**:
\[ 1.2 \times 120 = 144 \, \text{bar mL} \]

5. **Set up the equation to solve for \( P_2 \)**:
\[ 144 \, \text{bar mL} = P_2 \times 180 \, \text{mL} \]

6. **Rearrange the equation to isolate \( P_2 \)**:
\[ P_2 = \frac{144 \, \text{bar mL}}{180 \, \text{mL}} \]

7. **Calculate \( P_2 \)**:
\[ P_2 = \frac{144}{180} \]
\[ P_2 = 0.8 \, \text{bar} \]

### Final Answer:
The pressure of the gas in the 180 mL vessel at 35°C will be \( P_2 = 0.8 \, \text{bar} \).