To be transitive, the following has to be true:

**If** (a,b) and (b,c) are in the relation, **then** (a,c) must be in the relation.

For 1,2,3, and P, that statement is true. If you think it's not true, then you must have a specific example where (a,b) and (b,c) are in the relation but where (a,c) is not in the relation.

For Q it is not true. (1,2) and (2,3) are in the relation but (1,3) is not.