Please help me out.What is the difference between 'around' and 'round'
" The Earth revolves around(or round) the sun".
Which one is correct?
In your example, both are correct. For the prepositional uses, BrE tends to prefer round (around is perhaps more formal), AmE to prefer around. However, when used adverbially or as part of a phrasal verb, only one of the two words may be appropriate in both dialects, or in either. You really need to consult a good dictionary, eg the Oxford Advanced Learner's.