What is the volume of 0.20 moles of helium at STP?
A) 0.22 liters
B) 0.45 liters
C) 4.5 liters
D) 9.0 liters

Option (C) 4.5 liters

Explanation:

1mole of a gas occupy 22.4L at stp.

This implies that 1mole of He also occupy 22.4L at stp.

From the question given, we were asked to find the volume occupied by 0.20 mole of He at STP. This can be achieved by doing the following:

1mole of He occupied 22.4L.

Therefore, 0.2mol of He will occupy = 0.2 x 22.4L = 4.48 = 4.5L

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)