What makes a metal a good conductor of heat

Metals conduct heat well for two reasons: metal ions pack very closely together in their molecular lattice, and electrons drifting through the metal carry kinetic energy around the lattice. The result is a quick elevation in particle motion that is expressed through heat energy. This conductivity is one reason why one rarely sees metal playground equipment anymore — although the slides go a lot faster than plastic ones, sitting on a slide on a hot summer afternoon is often quite painful

Alpha particles have positive charge, beta particles have negative charge, and answer 4 just doesn’t make sense. thus, you are left with only one possible answer.