If n|m  means that n  is a factor of m , the relation | is

Since, n is a factor of n,  hence the relation is reflexive .Now, if, n is a factor of m,  but m is not necessarily a factor of n, so the relation is NOT SYMMETRIC.  On the other hand, if n is a factor of m and m is a factor of ℓ   then automatically, n will also be a factor of ℓ , so the relation is TRANSITIVE.