There are 5.5 moles of Argon gas in tank
Further explanation
Given
122.6 liters of Argon gas
Required
The number of moles
Solution
Assume at STP
Conditions at T 0 ° C and P 1 atm are stated by STP (Standard Temperature and Pressure). At STP, Vm is 22.4 liters / mol.
So for 122.6 L :
= 122.6 L : 22.4 L
= 5.47 moles ≈ 5.5 moles