Four number-pairs have been given, out of which three are alike in some manner and one is different. Select the one that is different.

73 - 79

THE LOGIC;

1) 31 - 41,

There is 1 prime number between them.

2) 83 - 97

There is 1 prime number between them.

3) 73 - 79

They are consecutive prime.

4) 61 - 71

There is 1 prime number between them.

Thus, 73 - 79 is the odd one.