Correct Answer: 2, 3, 4, 1

Solution : Given:
1. Billian 2. Bifurcate 3. Bilateral 4. Bilirubin

Step 1: Compare the first letter of each word. Since all the words start with the same letter B , then move on to the next letter.
Step 2: The second letter of each word is the same, i.e., i . So, move on to the next letter.
Step 3: The third letter of each word is either l or f . Based on the alphabetical order of these letters, we can arrange them – Bi f urcate, Bi l lian, Bi l ateral, Bi l irubin.
Step 4: Compare the fourth letter of (Bil l ian, Bil a teral, Bil i rubin). Bilateral will come before Billian and Bilirubin in the sequence as a comes before i and l in the alphabetical system. Similarly, Bilirubin will come before Billian as i comes before l in the alphabetical system.

So, the sequence is Bifurcate, Bilateral, Bilirubin, Billian, or 2, 3, 4, 1. Hence, the third option is correct.