The process of radioactive decay is unpredictable and irreversible. Which option would be an appropriate model of the radioactive decay of a group of atoms?.

before we can answer, we have to see the choices that are printed there with the question.   that's the only way we can point you to the correct one.

r=rho l/a where a is the area, l is the length and rho is resistivity so the greater the area the lesser the resistance thats why the earth pin is thicker bcos current follow the shortest path, so less resistive .