At STP the moles of helium gas present in 0.880L of vessel is 0.039 moles.
Moles of any gas will be calculated by using an ideal gas equation at STP as:
PV = nRT, where
P = pressure = 1 atm
V = volume = 0.880 L
n = moles of gas = ?
R = universal gas constant = 0.0820 L.atm / K.mol
T = absolute temperature = 273.15 K
On putting values we get,
n = (1)(0.880) / (0.082)(273.15)
n = 0.039 moles
Hence required moes of helium gas is 0.039 moles.
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