Correct Answer: 5, 3, 1, 6, 4, 2

Solution : Given:
1. Monorail   2. Monument   3. Monopoly   4. Monster   5. Monitor   6. Monsoon

Step 1: Compare the first letter of each word. Since all the words start with the same letter M , move on to the next letter.
Step 2: The second and third letters of each word are the same. So, move on to the next letter.
Step 3: The fourth letter of each word is o , u , o , s , i , s . Based on the alphabetical order of these letters, we can arrange them – Mon i tor, Mon o rail, Mon o poly, Mon s ter, Mon s oon, Mon u ment
Step 4: Compare the fifth letter of (Mono r ail, Mono p oly) and (Mons t er, Mons o on). Monopoly will come before Monorail in the sequence as p comes before r in the alphabetical system. Similarly, Monsoon will come before Monster as o comes before t .

So, the sequence is Monitor, Monopoly, Monorail, Monsoon, Monster, Monument, or 5, 3, 1, 6, 4, 2 . Hence, the fourth option is correct.