Q. Describe Critical Directive in FORTAN?

The critical directive permits one thread executes associated structured block. When one or more threads attain critical directive they would wait till no other thread is executing the same critical section (one with the same name) and then one thread would carry on to execute structured block. The syntax of critical directive is 

#pragma omp critical [name]

structured_block

name is optional. All critical sections with no name are regarded as to be one undefined name.