sir, am new to virtualization i just want to know the first Data Center Virtualization exam to take 1V0-620 OR 2V0-620?
Start your learning here: Virtualization Technology & Virtual Machine Software
Thinking about exams and certifications, you can review the objectives of each exam to help you decide what is best for you: Data Center Virtualization
VCA level certifications (and exams) are just fundamentals only, VCP level (and exams) are fairly technical and you will also need to take training.
You also asked about the 1V0-621 and 2V0-621 exams - as the question was so similar to what you've asked in this thread, I've deleted that thread as it can be answered here.
Those 2 exams are for totally different certifications - 1V0-621 is the exam for VCA6-DCV, while 2V0-621 is for VCP6-DCV.
I strongly recommend you take a look at this page to learn more about the certifications: Data Center Virtualization