Question

why rutherford used for gold foil is above said experiment

Answer 1

Rutherford used gold foil because it can deviate the alpha ray particles

Answer 2

Gold is extremely malleable and can be beaten into very extremely thin sheets. This would give more observations as the alpha particles would be deflected by less no. of layers of atoms. Also, gold nuclei are relatively heavier than alpha particles and would not be themselves displaced when alpha particles come near.