Final answer:
Mercury-203 undergoes beta minus decay to become thallium-203. The atomic number increases by one to 81, and the mass number remains at 203. The decay process is represented by the nuclear equation 20380Hg → 20381Tl + 0-1β-.
Step-by-step explanation:
Mercury-203 undergoes beta minus decay, which is a type of radioactive decay where a neutron in the nucleus of an atom is transformed into a proton while releasing a beta particle (an electron) and an antineutrino.
The atomic number of Mercury (Hg) is 80, and when it decays, it transforms into thallium (Tl), with the atomic number increasing by 1, making it 81. The mass number remains unchanged at 203.
The nuclear equation for this decay process is:
20380Hg → 20381Tl + 0-1β-
Here, the beta particle (β-) is represented by an electron with an atomic number of negative one (-1) and a mass number of zero, as the electron's mass is negligible compared to that of protons and neutrons.