Atomic theory states that all substances are comprised of atoms. Something that has all the same atoms is an element; something with a mixture of different atoms is a compound. Each of these (elements and compounds) have electrons zipping around them; In general, its these electrons that determine if a reaction takes place between two substances. If conditions are right, a transfer of electrons from one substance to another occurs, and a reaction happens.
Whether or not a reaction takes place is contingent upon the relative electron arrangements of the substances being combined, and how tightly or loosely those electrons are held.
the question above is wrong because all substances atrract which each other but some attract more while others attract very less their attraction is not noticible. for example mercury has a very strong force of attraction between its particles therefore when we put our finger in mercury the force of attraction is very less between mercury and our finger which prevents our finger to get wet.