We can find the number of moles of water at STP conditions using the ideal gas law equation
PV = nRT
Where P - standard pressure - 1 atm
V - 22.4 L
n - number of moles
R - universal gas constant - 0.0821 L.atm/mol.K
T - standard temperature- 273 K
Substituting the values in the equation
1 atm x 22.4 L = n x 0.082057 L.atm/mol.K x 273 K
n = 1.00 mol
Therefore number of water moles are 1.00 in 22.4 L
This is called the molar volume, 1 mol of any gas occupies a volume of 22.4 L at STP
Molar mass of H2O is 18.02 g/mol
Mass of water is 18.02 g/mol
Answer is A. 18.02 g/mol