Answer:
30.9 g He
Step-by-step explanation:
To find the mass of the helium (He) sample, you need to
(1) convert atoms to moles (using Avogadro's Number)
(2) convert moles to grams (using the atomic mass of He)
It is important to arrange the conversions/ratios in a way that allows for the cancellation of units. The final answer should have 3 sig figs like the given value (4.65 x 10²⁴ = 3 sig figs).
Avogadro's Number:
6.022 x 10²³ atoms = 1 mole
Atomic Mass (He): 4.0026 g/mol
4.65 x 10²⁴ atoms He 1 mole 4.0026 g
-------------------------------- x -------------------------------- x ----------------- = 30.9 g He
6.022 x 10²³ atoms 1 mole