Answer:- There are 0.337 moles of the gas.
Solution:- Volume(V) of carbon dioxide gas = 7.5 L
Conditions are STP means, T = 273 K and P = 1 atm
From ideal gas law equation, PV = nRT
n = PV/RT
Where n is the number of moles and R is the universal gas constant and it's value is 0.0821 atm.L/mol.K
Let's plug in the values in the formula..
n = (1 x 7.5)/(0.0821 x 271)
n = 0.337 mol