Number of query-response pairs = 4.
The name of the url is www.gate.org.in and not www.gate.in.
If it was www.gate.in , then there would have been 3 pairs because of 3 levels, namely, root DNS server, TLD server for .in and Authoritative server.
But given URL is www.gate.org.in and so there will be 4 pairs because of 4 levels, namely, root DNS server, TLD server for .in, TLD server for .org and the authoritative server.
It should be noted that the iterative query can have more than 3 levels and it is not necessary that whatever be the URL, number of levels have to be exactly 3. It can be more than that.