Why Ruthrford selected a gold foil for his experiment?
2. The use of gold had nothing to do with its reactivity, any more than the experiment had any connection to chemistry. Rutherford wanted to fire alpha particles through the foil. Alpha particles are not very penetrating; a sheet of notepaper will stop most of them. To achieve a reasonable percentage of penetration the foil needed to be really thin.
Gold is highly malleable; gold leaf can be made in thicknesses around 100 nm or 4 micro-inch. It was the best material for the job.