Which option is an element
A: carbon dioxide
B: Water
C: Air
D: Carbon

carbon is an element (D)

Explanation:

An element is a substance composed of a single type of atom. In this case, only carbon is an element.

conduction is the transfer of thermal energy (heat in transfer) due to collisions between the molecules in the object. collisions between adjacent atoms and molecules transfer kinetic energy from the warmer to the cooler object. the objects must be in physical contact.

that's what i got you can count the number of atoms