eragera@Era-PC:~$ apt-cache policy gtk-sharp2; sudo apt install gtk-sharp2
gtk-sharp2:
  Installed: (none)
  Candidate: 2.12.10-6
  Version table:
     2.12.10-6 500
        500 http://in.archive.ubuntu.com/ubuntu xenial/universe amd64 Packages
        500 http://in.archive.ubuntu.com/ubuntu xenial/universe i386 Packages
[sudo] password for eragera:
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 gtk-sharp2 : Depends: libglade2.0-cil-dev (= 2.12.10-6) but it is not going to be installed
              Depends: libglib2.0-cil-dev (= 2.12.10-6) but it is not going to be installed
              Depends: libgtk2.0-cil-dev (= 2.12.10-6) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
eragera@Era-PC:~$