1. Is birth certificate compulsary ? can a secondary school certificate (10 or 10+2)indicating date of birth will do in its place.
[A] Sorry, can't help u on this one. Better ask someone from your own country.
2.can u tell about original transcripts in university sealed envelopes? are degree certificates not sufficient.Transcripts for spouse is also necessary or only diploma d=certificates will do.
[A] I don't think university sealed envelopes are required. In my case, I submitted copies of certificates + marksheets notarized by a Barrister. CHC has accepted it (I'm on medical stage now). You should also submit copies of marksheets (basically transcripts but not in a sealed envelope). Please check instructions which are specific to your visa office and follow them.
3.only experience letter will do from previous and current employer or appointment letter is also to be given.I donot have the appointment letter.
[A] Not an issue. As long as there is no doubt about the authenticity of your experience letter and your employment in their company, this should not be a problem.
4. are experience letter and reference letter the same from the current employer
[A] Name of the letter doesn't matter. You can even call it "French Letter" if u like

please ensure necessary information required by the visa office (Designations held, duration of service, salary, work description etc. etc. is included in it.
5. Business card is same as visiting card of the employer?
[A] British and former british colonies use the word "visiting card" more often than the americanized word 'business card'. Actually in old old days, visiting card was a card used by aristocracy, which contained the name only. If you were an aristocrat visiting another aristocrat's mansion, you were supposed to hand over the visiting card to the butler at the door. Nowadays, its the same as business card (which contains name, address, phone no. e-mail etc.)