Suppose a system has 12 instances | UGC NET Dec 2018

Q2. UGC NET Dec 2018 : 

Suppose a system has 12 instances of some resource with n processes competing for that resource. Each process may require 4 instances of the resources. The maximum value of n for which the system never enters into deadlock is
a) 3
b) 4
c) 5
d) 6
What is Deadlock ?
Ans. Deadlock is a situation where set of processes are blocked because each process holding a resource and waiting to acquire a resource held by another process. 
Number of instances = 12
Number of processes = n
Each process requires = 4 instances
1 process occupy = 4 instances
2 process occupy = 8 instances
3 process occupy = 12 instances.
No resource remaining for more than 3 process.
So the maximum number of processes is 3.
Option a) 3 is the correct answer.