Hi,
According to Bohr's postulates we can state that:The angular momentum of an electron in a given stationary state can be expressed as:

mevr=n2h

whereme=mass of electron,v=velocity of electron,r=radius of Bohr orbit,n=nthBohr orbit (Integral value)

Thus an electron can move only in those orbits for which its angular momentum is an integral multiple of2hthat is why only certain fixed orbits are allowed.

This explains the stability of an atom by giving a condition for an allowed orbit.

Hey,

If we consider the postulate of Bohr, we get to know that,

In a stationary state, the angular momentum of any electron can be demonstrated by the equation:

m*v*r=n*2*π*h

here,

m=mass of electron

v=velocity

r=radius of Bohr's orbit

n=the nth Bohr orbit which is an Integral value

Thus through this we get to know that, electrons can move only in those orbits for which its angular momentum is an integral multiple of h/2π.

This condition also explains the stability of an atom.

I hope this helps.

All the best!