It seems that nitrogen is, but its odd tbh.
Neutrons.
Not sure if you need a full explanation but let me know if you do :]
I think it is the first choice
Hope that helped!
The answer is definitely D
Definition: Cubic centimeter. A cubiccentimetre (cm3) is equal to thevolume of a cube with side length of 1 centimetre. It was the base unit ofvolume of the CGS system of units, and is a legitimate SI unit. It is equal to a millilitre (ml).
Convert ml to cm cubed - Conversion of Measurement Units