> A system has 6 identical resources and $N$ processes competing for
> them. Each process can request atmost 2 requests. Which one of the
> following values of $N$ could lead to a deadlock?
> 
>  1. 1
>  2. 2
>  3. 3
>  4. 4

----------
My attempt :

Deadlock free condition is :

$R  \geq P(N-1)+1 ,$

Where R is total number of resources ,

P is the number of processes , and 

N is the max need of each resource .

$6 \geq P(2-1) + 1$  
$6 \geq P + 1$  
$5 \geq P$ 

So , number of processes should be less than $5$ for deadlock free condition. 

Hence, all options can not be deadlock .


----------
In this exercise problem  answer given option (4). 

>Can you explain in formal way, please?