Find the number of atoms of argon in 12.0 L of argon at STP

3.25x10^23mol

Explanation:

1 mole of argon = 22.4dm^3

X mole of argon = 12.0L

X 22.4 = 12.0

X = 12.0/22.4

X = 0.54mol

1 mol of argon contains 6.02x10^23 atom

Therefore 0.54 mole will contain X

Therefore X = 6.02x10^23 x 0.54

= 3.25x10^23mol