a) Who discovered the nuclear model of the atom?
b) Explain how Rutherford's atomic structure cannot explain the stability of atom?

a) Rutherford was the first scientist to give the nuclear model of the atom. His descriptions that nucleus is present at the centre of the atom is unquestionable even today.
b) But Rutherford's description that electrons move is different circular orbits, round the nucleus is not correct, as such, motion leads to the instability of the atom. This is because an electron moving in a circular orbit should accelerate. Further an electron, possessing a negative charge, when accelerated, should radiate energy and thus a moving electron goes on losing its energy and hence it is gradually attracted by the nucleus, consequently it falls into it, leading to instability.