Let us denote by the letter N the number of atoms contained in a helium gas of mass m = 1r = 0.001 kg. It is known that any substance taken in an amount of 1 mol contains N (Avogadro) = 6.02 x (10 ^ 23) particles. The mass of 1 mol of helium is determined according to the periodic table M = 0.0040026 kg / mol. Obviously, the number of moles of a substance is determined in two ways, that is, ν = N: N (A) or ν = m: M, we get the proportion m: M = N: N (A), then N = (m • N (A) ): M. Substitute the found values of physical quantities and make calculations N = (0.001 kg • 6.02 • (10 ^ 23) 1 / mol): 0.0040026 kg / mol. N = 1.5 • (10 ^ 23) atoms.
Answer: N = 1.5 • (10 ^ 23) atoms in 1 g of helium.
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