How many molecules are in 2L of water vapor at STP?

Question

I need the full equation to fully answer the question please

Answer 1

At STP 1 mole of an ideal gas = 22.4 liters. Assuming that water vapor behaves as an ideal gas, then...

2 L x 1 mole/22.4 L = 0.08929 moles

0.08929 moles H₂O x 6.02x10²³ molecules/mol = 5.4x10²² molecules = 5x10²² molecules (1 sig. fig.)