I have sonar qube 6.1 installed but when we integrate with TFS, it is not analyzing all the projects but skipping some projects. Also can you let me know maximum no of solutions sonar qube can analyze at a time?
6.1 is waaay past EOL at this point. The current version is 8.3 (8.4 imminent) and the current LTS is 7.9.3.
Your upgrade path is:
6.1 -> 6.7.7 -> 7.9.3 -> 8.3
You should upgrade at your earliest convenience.