The question tests the understanding of the definition of a null set provided in the context ('A set which does not contain any element is called the empty set'). For option (i), odd numbers are never divisible by 2. For option (iii), the conditions x < 5 and x > 7 are contradictory. For option (iv), parallel lines have no intersection. All three result in sets with no elements. Option (ii) is not a null set because the context explicitly mentions '2 is the only even prime number', meaning the set contains one element.