Answer : The number of moles of helium gas found in a balloon are 0.26 moles.
Explanation :
To calculate the moles of helium gas, we use the equation given by ideal gas :
PV = nRT
where,
P = Pressure of helium gas = 1.15 atm
V = Volume of the helium gas = 5.5 L
n = number of moles of helium gas = ?
R = Gas constant =

T = Temperature of helium gas =

Putting values in above equation, we get:

Therefore, the number of moles of helium gas found in a balloon are 0.26 moles.