A relation is a function if & only if for each value of x we have (at the most) one & only one value of y. In short if we have a repeat value of x that correspond to 2 different values of y then it's not a function but a relation instead
Let's take the 1st example: x I y ---------I------- 1 I 2 3 I 2 3 I 3 4 I 2 We notice that there are 2 SAME VALUE of x (that is 3) that have various value of y, Hence this is not a function. Mind you this concerns x ONLY. In short a function doesn't allow a repeat of same x. Follow this methodology & you will find the other problems