I was studying Bohr's atomic model and came to know that when electrons make transitions in between the orbits they lose or gain energy in the form of electromagnetic radiations. I understand why they lose or gain energy. But why is it only in the form of electromagnetic radiations and in not any other form?
Actually other forms of energy could be emitted or absorbed. These are the Raman lines. Sometimes a raman line corresponds to transfer of part the energy into the internal rotational/vibrational states. In a solid this would correspond to part of the energy bring emitted as a phonon. Sometimes a phonon energy is added to the energy if the incoming photon and one gets a higher energy photon as the output
Ofcourse phonons are bosons just like photons
The issue of emission or absorption of electromagnetic radiation by an atom, within Bohr's atomic model, goes the other way around.
The model was introduced by Bohr to provide a unifying picture where stability of motion of an electron moving around the nucleus (thus being an accelerated charge which should emit e.m. radiation, according to Maxwell's equations) and the experimental evidence of line spectra of atoms could coexist. Bohr's model explicitly eliminates e.m. radiation of the orbiting electrons, with the only exception of transition from an orbit to another.
Other conversion of energy when electrons jump, at least in the case of an isolated atom are hard to imagine.