Choose statements in context of monitor based synchronization scheme that use condition type variable x:

I: Only wait () and signal () operations can be involved on X.

II: If process p invokes X, wait() operation; then P is suspended until another process invokes X, signal().

III: The X, signal() operation resumes exactly one suspended process and if no process is suspended, the it has no effect.

The monitor is one of the ways to achieve Process synchronization. The monitor is supported by programming languages to achieve mutual exclusion between processes.

• The operation x.wait(); means that the process invoking this operation is suspended until another process invokes x.signal();.
• The x.signal operation resumes exactly one suspended process.  If no process is suspended, then the signal operation has no effect.

Wait operation

wait() : Process performing wait operation on any condition variable are suspended. The suspended processes are placed in block queue of that condition variable.

Signal operation

signal(): When a process performs signal operation on condition variable, one of the blocked processes is given chance.

Hence Option 4 is correct