Which has more mass? a
1 mole of Carbon
b
1 mole of Oxygen
c
1 mole of Chlorine
d
1 mole of Hydrogen

Chlorine has more mass than the other elements.

Explanation:

We can find the mass of each element using the following equation:

Where:

η: is the moles

A: is the standard atomic weight

a) For carbon, we have:

b) For oxygen, we have:

c) For chlorine, we have:

d) And for For hydrogen, we have:

Therefore, chlorine has more mass than the other elements.  

I hope it helps you!