Question

Balloons are often filled with helium gas
because it weighs only about one-seventh of
what air weighs under identical conditions.
The buoyancy force, which can be expressed
as

Answer 1

The buoyancy force can be expressed as

$F_b = \rho_{air} g V_{balloon}$ or, taking into account condition $\rho_{He} = \rho_{air} /7$ ,

$F_b = 7\rho_{He}g V_{balloon}$ .