Answer:
2.50x10²¹ atoms
Explanation:
First we convert the given mass of dimercaprol to moles, to do so we calculate its molar mass:
515 mg equal 0.515 g
As one dimercaprol molecule binds to one As atom, one mol of dimercaprol reacts with one mol of As.
So we convert those 4.146 x 10⁻³ mol of As to atoms, using Avogadro's number: