In nuclear physics, beta decay is one of the types of radioactive decay where a beta particle (which could be an electron or a positron) is emitted from the atomic nucleus. It occurs when a nucleus with a high amount of protons or neutrons and one of the protons or neutrons is transformed into the other. For mercury 202 there is not much information about its decay, it is believed that it will undergo decay into Pt-198 in alpha decay, so let's write the equation for beta decay
202/80Hg, I will use this notation to represent atomic mass/atomic number
202/80 Hg -> 202/81 Tl + 0/-1 e + 0/0 y
Where:
Mercury will undergo the decay and become Thallium-202, as we can see by the increase of protons, one beta particle (e) is released and y is the antineutrino particle, also essential in a beta decay