A spherical balloon of radius 25 cm is filled with hydrogen gas. The volume of a sphere of radius r is `(4/3)*pi*r^3` .
The volume here is `(4/3)*pi*r^3 = (4/3)*pi*25^3` = 0.0654 m^3 = 65.4 liters. Assume the gas in the balloon is at STP, 1 mole of hydrogen has a volume 22.4 liters. Its mass is 2 g.
The mass of 65.4 liters is 5.84 g. The mass of the rubber balloon is 20 g.
The total mass of the balloon filled with hydrogen is 25.84 g