Step 1: Understanding biological testing.
Biologicals, such as vaccines, are tested in designated testing centers. In India, the Central Drugs Laboratory located in Kasauli is responsible for testing biological products for safety, efficacy, and quality.
Step 2: Analyzing the options.
(1) Mumbai: Incorrect, Mumbai does not host the primary testing center for biologicals.
(2) Kolkatta: Incorrect, Kolkatta is not the center for testing biologicals.
(3) Chennai: Incorrect, biological testing is not carried out in Chennai.
(4) Kasauli: Correct — Kasauli houses the Central Drugs Laboratory, where biologicals are tested.
Step 3: Conclusion.
The correct answer is (4) Kasauli.