Question

Why did Rutherford select a gold foil in his alpha-ray scattering experiment?

Answer 1

Gold is a heavy metal with high mass number. A light metal cannot be used because, on being hit by fast moving a-particle, the atom of light metal will be simply pushed forward and no scattering can occur. Moreover, gold is the best malleable metal. A very thin foil (=1000 atoms thick) can be made from gold to get the clear observations.