The volume of the balloon can be calculated using the ideal gas law:
V = nRT/P
where:
n = number of moles of gas (0.77 moles in this case)
R = the ideal gas constant (0.08206 L·atm/(mol·K))
T = temperature in Kelvin (36°C + 273.15 = 309.15 K)
P = pressure (1 atm)
Plugging in the values, we get:
V = (0.77 mol)(0.08206 L·atm/(mol·K))(309.15 K)/(1 atm) ≈ 19.7 L
the volume of the balloon is approximately 19.7 liters.