1. Hydrogen gas was cooled from \( 150^{\circ} \mathrm{C} \) to \( 50^{\circ} \mathrm{C} \). Its new volume is \( 125 \mathrm{~mL} \). What was its original volume?

Step 1 ：\( T_1 = 150^{\circ} \mathrm{C} = 423.15 \mathrm{K} \)

Step 2 ：\( T_2 = 50^{\circ} \mathrm{C} = 323.15 \mathrm{K} \)

Step 3 ：\( V_1 = \frac{V_2 \times T_1}{T_2} = \frac{125 \mathrm{mL} \times 423.15 \mathrm{K}}{323.15 \mathrm{K}} \)