Which of these is an element?

A. Oxygen

B. Sodium Chloride

C. Water

D. Air

Hello!

An "element" is a substance that is made entirely of one type of atom. Out of the four given options, A. Oxygen is considered an element, because it just can't be broken down farther. As for the other options, Sodium Chloride and water are both compounds, not elements. Air is a mixture.

It looks like your answer is A. i mean A and B are both elements.