How many C2H4 molecules are contained in 7.44x10^-18 mg of C2H4?

Question

How many C2H4 molecules are contained in 7.44x10^-18 mg of C2H4? The molar mass of C2H4 is 28.05 g/mol.

Answer 1

Dimensional analysis:

7.44x10^-18 mg x 1 g/10³ mg x 1 mol/28.05 g x 6.02x10²³ molecules/mole = 1.60x10² molecules