The total pressure of a mixture of non-reacting gases X(0.6 g) and Y(0.45 g) in a vessel is 740 mm of Hg. The partial pressure of the gas X is mm of Hg. (Nearest Integer)
(Given: molar mass X = 20 and Y = 45 g mol$$^{-1}$$)

Finding the moles of each gas:

$$ n_X = \frac{0.6}{20} = 0.03 \text{ mol} $$

$$ n_Y = \frac{0.45}{45} = 0.01 \text{ mol} $$

Total moles: $$n_{\text{total}} = 0.03 + 0.01 = 0.04$$ mol

Mole fraction of gas X:

$$ \chi_X = \frac{n_X}{n_{\text{total}}} = \frac{0.03}{0.04} = 0.75 $$

Partial pressure of gas X (by Dalton's law):

$$ P_X = \chi_X \times P_{\text{total}} = 0.75 \times 740 = 555 \text{ mm of Hg} $$