I think that the answer is d
Answer:
4.52 x 10²⁴ atoms Cl
Explanation:
A mole is a name that means a certain number like a dozen means 12. 1 mole of chlorine atoms is 6.022 x 10²³ chlorine atoms. The unit conversion is 6.022 x 10²³/mol.

Round to 4.52 x 10²⁴ atoms Cl for the correct number significant figures.
Answer:
OXYGEN
I don't know what to say for the 20 character limit