The molar mass of helium (He) is 4.0026 g/mol. This means that 15 g of helium is equal to 15 g / 4.0026 g/mol = 3.747 mol of helium.

The volume occupied by a gas can be calculated using the ideal gas law:

PV = nRT

where:

P is the pressure of the gas

V is the volume of the gas

n is the number of moles of gas

R is the ideal gas constant (8.314 J/mol*K)

T is the temperature of the gas

Assuming that the pressure and temperature are 1 atm and 273 K (standard temperature and pressure), we can calculate the volume occupied by 15 g of helium:

V = nRT/P

V = (3.747 mol)(8.314 J/mol*K)(273 K)/1 atm

V = 83.1 L

Therefore, 15 g of helium gas occupies a volume of approximately 83.1 liters at standard temperature and pressure.