If its atomic number is 48, then it has 48 protons in the nucleus of each atom. Any more mass than that is supplied by the neutrons that are mixed in there with the protons.
If the mass is 167, and 48 of those are protons, then there are
The voltage across the bulb is the voltage across the batteries, since the batteries are the only source of power for the bulb. So the voltage across the batteries is 3.0 V.
