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

Solution : Given:
1. Tertiary 2. Terrace 3. Terrain 4. Termite 5. Territory 6. Terminate

Step 1: The first, second, and third letters of each word are the same, so move on to the next letter.
Step 2: The fourth letter of each word is t , r , r , m , r , m . Based on the alphabetical order of these letters, we can arrange them – Ter m ite, Ter m inate, Ter r ace, Ter r ain, Ter r itory, Ter t iary.
Step 3: Compare the sixth letter of (Termi n ate, Termi t e) and the fifth letter of (Terr a ce, Terr a in, Terr i tory). Terminate will come before Termite in the sequence as n comes before t in the alphabetical system. Similarly, Terrace and Terrain will come before Territory.
Step 4 : Compare the sixth letter of (Terra c e, Terra i n). Terrace will come before Terrain in the sequence as c comes before i in the alphabetical system.

So, the sequence is Terminate, Termite, Terrace, Terrain, Territory, Tertiary, or 6, 4, 2, 3, 5, 1. Hence, the third option is correct.