Most of the times, those 4 mark questions dont really need to be that detailed. Like one paragraph will do. 5 6 markers are a bit more, so you most of the time need to start crapping on a tangent. Underline the keywords, i.e. 'hydrogen spectrum. mathematical model. Bohr.'- and then talk about as much as you know about these if you have difficulty answering the question directly.
You might also want to consider spelling Bohr Bohr. : P
That's the lazy way out, or you could really synthesise it.
Bohr's model explained with theory as well as experiment the mathematical models for the hydrogen spectrum. By using his postulates, he rederived Balmer's empirical equation, hence confirming both the eqaution and his theory. Using his model, an expression for the wavelengths of the hydrogen spectrum could be derived. < insert Rydberg's equation >
