The answer is the last one (it needs a medium through which to travel) it is not true about radiation. A radiation is the emission of energy in the form of waves or particles through space or through a material medium. This includes; electromagnetic radiation, such as a radio wave, microwaves, visible light, x rays, and gamma radiation.
I think it is carbon dioxide
Different explanations that lead to the same result
-You need to substract the number of protons from the mass number.
-Mass number - atomic number= number of protons
-Following this equation:
CARBON
atomic number= 6
mass number= 12
mass number= protons + neutrons
12= 6 + x
x= 12-6
x= 6