In early 2016, platinum (195.078 g/mol) was selling for about $1062 per troy ounce (one troy ounce is equal to 31.10 g).How many platinum atoms could you buy for $20?

Question

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The correct answer is A because:1 troy ounce = 31.10 g$1062 / 31.10 g = $34.15 / g$20 / $34.15 / g = 0.5856 g0.5856 g / 195.078 g/mol = 0.002999 mol0.002999 mol * 6.022 * 10^23 atoms/mol = 1.808 * 10^21 atoms

In Early 2016, Platinum (195