Answer:
Step-by-step explanation:
Comment
You have to look around for the best R to use. The problem is that R has different values depending on what the units of the givens are. In this case you have
Givens
V = 45 L
P = 1.01 atmospheres
T = 25 degrees = 25oC + 273 kelvin = 298 degrees kelvin
R = 0.08206 for those givens.
Equation
PV = n * R * T
Solve
1.01 * 45 = n * 0.08206 * 278
n = (1.01 * 45) / (0.08206*278)
n = 1.99