1.Why rutherford use gold foil only?

2.Why bohr`s model can`t explain continous spectrum?

Dear Student!

The foil used by Rutherford was supposed to be very thin, so that most of the rays passed through and a few deflected. Only Gold is that malleable to form such foils, hence it was used.

It is incorrect to say that Bohr's theory could not explain the continuous spectra. Infact it did, but only  of Hydrogen nuclei only and was inadequate for heavier atoms.