How many moles are there in:
56.4 l of helium gas (he) at stp

1 mole He 22.4 L ( at STP)
( moles He ) 56.4 L

moles He = 56.4 x 1 / 22.4

moles  He = 56.4 / 22.4

= 2.517 moles of Helium gas

We know, there is 1 mole at 22.4 Liter [ STP ]
Number of moles at 1 Liter = 1 / 22.4

Now, at 56.4 Liter, it would be: 1/22.4 * 56.4 = 2.52 moles

In short, Your Answer would be 2.52 moles

Hope this helps!

Thermohaline circulation and gyres