Question

Which is an element? A: H20 B: NaCl C: Mg D: CO

Answer 1

D is the answer. The others are compounds not single elements

Answer 2

The answer is option D "CO." Co also known as Cobalt is the 27th element on the periotic table. It was discovered in 1735, it's boiling point is 3200 k.

Atomic mass: 58.9332
Protons: 27
Neutrons: 32
Electrons: 27

Hope this helps!