Step 1: Understanding Article 16.
Article 16 of the Constitution of India deals with equality of opportunity in matters of public employment. Clause (4B) was inserted to allow the unfilled reserved vacancies of a year to be carried forward to subsequent years.
Step 2: Constitutional Amendment.
Clause (4B) was inserted by the 81st Constitutional Amendment Act, 2000. This amendment ensured that the total number of reserved vacancies could exceed 50% in a particular year due to backlog vacancies.
Step 3: Conclusion.
Thus, Clause (4B) of Article 16 was introduced by the 81st Amendment Act.