I have searched a lot but I didn't get the reason that even after giving the IP address it never shows the DNS. If it doesn't give the DNS then why it is said to be reverse IP lookup?
Reverse DNS is a term for looking up the DNS PTR record for an IP address - essentially resolving it 'backwards' to a host name (in contrast to 'forward' resolving a host name to an IP address using the A record).
While this should be supported everywhere, it often isn't due to a lack of setup or to security concerns. You'll need to set up your DNS correctly (off-topic here) or contact your network admin if you think that is a problem.