Odd one out: Concepts & Solved examples

This is a comparatively easier topic. In this, out of the given options, you have to choose, which one is different or odd one out, i.e. one which is not related to others   
How to find odd object
The idea is to solve it with the help of basic common sense, but broadly speaking we can identify the different one or odd one out by following categories:
  1. Even or Odd
  2. Gender
  3. Use and the applicability of the object.
This concept could be understood by following examples:
Directions for questions 1 to 7: In each of following examples, four words have been given of which three are alike in some way and one is different. Choose the odd one out. 
Example No. 1: pen, pencil, marker, eraser
Solution: Except eraser, rest all are used for writing.
Example No. 2: 71, 73, 79, 91
Solution: Except 91, rest all are prime numbers. Hence odd one is 91.
Example No. 3: Book, eraser, pen and compass.
Solution: Book is not stationery item while rest all are stationery items. Hence book is the odd one out.
Example No. 4: Onions, garlic, radish, cauliflower
Solution: Here all the vegetables grow underground except cauliflower. Therefore cauliflower is the answer.
Example No. 5: Agra, Vrindavan, Ambala, Bhopal.
Solution: Only Bhopal is Capital. Thus Bhopal is the answer.
Example No. 6: Jacket, Sweater, Coat, Tshirt
Solution: Except Tshirt all are winter wears.
Example No. 7: Cabbage, Apple, Apricot, Banana
Solution: Here all the objects are fruits except Cabbage, which is a vegetable.