Three of the four pairs of words given below are alike in a certain way and thus form a group. Which is the one that does not belong to the group?

Correct option is C

A) Ice-cube : Cold
Ice-cube is an object and cold is its natural property.
B) Iron : Hard
Iron is an object and hard is its natural property.
C) Smooth : Marble
Smooth is a property, while marble is an object. The order is different from the other pairs.
D) Dough : Soft
Dough is an object and soft is its natural property.
Thus, the pair that does not belong to the group is option (C).