The mass of an atom of uranium is 4
10-25 kg.
What is the mass, in milligrams, of 8 million atoms of uranium?

Answer:

2) E

Mass of 8×10⁶ uranium atoms = 4 x 10⁻²⁵ x 8 x 10⁶
(32 x 10⁻¹⁹) kg = (32 x 10⁻¹³) mg

Answer: 3.2 x 10⁻¹² mg