Q. Describe classical model of macroeconomics?

Though we use the term ‘the classical model' as if there were just one classical model, this isn't quite true. For all the models we discuss, there are many variations. Though the similarities between, for instance, all the classical models are great enough to warrant expression ‘the classical model'.

However you need to keep this in mind. If you look up the ‘IS-LM model' in different text books you will probably see different models though the main predictions from the models do tend to be the same.