Sir, i have a problem in speaking (specially words containing 's' , 'z', 'r' etc...) due to my large tongue. can u suggest me the cure for this?

Speech therapy : Best bet, so see your doctor for a referral. Your doc will also help to rule out other contributing factors.

Large tongue: If your large tongue is genetic and not due to some treatable condition then i would seek an oral surgeon to discus your options and pro/cons. If it is a condition there may be a treatment to diminish the size of your tongue, but an oral surgeon or knowledgable dentist would be able to help you with that.

See Oral Surgeon: It may not be the size of your tongue , but the position of your teeth an/ or a lingual frenum problem, preventing total movement. An oral surgeon, and perhaps orthodontist should be consulted!