Answer
0.28 L PH3
Work Step by Step
The volume of one mole of gas at STP is 22.4 L. Use this as a conversion factor to convert from liters to moles of hydrogen. Use a mole ratio based on the stoichiometric coefficients to convert from moles of hydrogen to moles of phosphine. Then use the volume of a gas at STP to convert from moles to liters of phosphine.