1.  Is there any difference between following declarations? 

1 : extern int fun(); 
2 : int fun();
A. Both are identical
B. No difference, except extern int fun(); is probably in another file
C. int fun(); is overrided with extern int fun();
D. None of these

Answer: Option B

Explanation:

extern int fun(); declaration in C is to indicate the existence of a global function and it is defined externally to the current module or in another file.

int fun(); declaration in C is to indicate the existence of a function inside the current module or in the same file.