Q.State the two postulates of Bohr's model of the hydrogen atom that

Bohr's model rests on a small number of postulates, of which two directly quantise the electron's motion.

Quantisation of angular momentum. Only those circular orbits are allowed for which the electron's orbital angular momentum is an integral multiple of $h/2\pi$:

Here $m$ is the electron's mass, $v$ its speed, $r$ the orbit radius, $h$ Planck's constant, and $n$ the principal quantum number labelling the orbit. Only these particular combinations of $r$ and $v$ are permitted; every other orbit is forbidden.

Stationary (non-radiating) orbits. As long as the electron remains in one of these allowed orbits, it does not emit electromagnetic radiation, even though classical theory says an accelerating charge (and a circling electron is accelerating, since its direction keeps changing) must continuously radiate energy and spiral inward. Bohr simply postulated that this classical expectation does not apply to these particular orbits, which is exactly what keeps the atom stable and allows the electron to occupy a fixed orbit indefinitely.

Energy is emitted or absorbed only when the electron jumps between two allowed orbits, with the photon's energy exactly equal to the energy difference between them -- this third postulate is what reproduces the hydrogen line spectrum.

Recall Bohr's postulates directly: the quantisation condition on angular momentum, and the stability (non-radiation) condition on a stationary orbit.

Confusing the quantisation-of-angular-momentum postulate with the (separate) energy-emission postulate that governs transitions between orbits; forgetting that $n$ must be a positive integer.