Two balloons are kept at room temperature and pressure, one holding Br2 gas, and one holding He gas. Each balloon is occupying 1.0 L at 273 K and 1 atm of pressure. If R = 0.0821 L*atm/mol*K, what is the:
a) Number of grams of gas in each balloon?
b) Density (mass per volume) of gas in each balloon?