Question

A volume of 56.0 mL of He at STP. a. Contains how many molecules?

Answer 1

0.0025 molecules or 2.5*10^-3 molecules

At STP one mole of gas is equal to 22.4L, so how many moles would 56.0 mL have?

1 mole = 22.4L

x moles = 0.056 L

x = 0.0025 moles.