Examine each of the following relations given below and state in each case, giving reasons whether it is a function or not? (i) \( R = \{ (2,1), (3,1), (4,2) \} \), (ii) \( R = \{ (2,2), (2,4), (3,3), (4,4) \} \), (iii) \( R = \{ (1,2), (2,3), (3,4), (4,5), (5,6), (6,7) \} \)