Step 1: Read the question.
We must find the amendment that added Clause (4B) to Article 16.
Step 2: Recall what Article 16 covers.
Article 16 deals with equal opportunity in public jobs, including reservation provisions.
Step 3: Understand Clause (4B).
Clause (4B) allows reserved vacancies left unfilled in one year to be carried forward to the next year as a separate group. This lets the carried-forward seats stay outside the usual ceiling for that year.
Step 4: Match it to the amendment.
The 81st Constitutional Amendment Act, 2000, added this carry-forward rule for unfilled reserved vacancies.
Step 5: Eliminate the others.
The 85th amendment dealt with consequential seniority in promotions. The 88th dealt with service tax. The 92nd added languages to the Eighth Schedule. None added Clause (4B).
Step 6: Conclude.
The correct answer is the 81st Constitutional Amendment.
Answer: 81st Constitutional Amendment