JEE Main 2021 · 27 July · evening · Single correct · +4 / −1
Given below are two statements :
Statement I : Penicillin is a bacteriostatic type antibiotic.
Statement II : The general structure of Penicillin is :
Choose the correct option :
- (a) Both statement I and statement II are false
- (b) Statement I is incorrect but statement II is true
- (c) Both statement I and statement II are true
- (d) Statement I is correct but statement II is false
Answer and solution
Answer (b) Statement I is incorrect but statement II is true
Solution
Chemistry ma’am · 4 steps
Penicillin kills bacteria outright, and the drawn ring system is the true penicillin skeleton.
- Statement I. A bactericidal antibiotic kills bacteria, while a bacteriostatic one only stops them from growing. Penicillin blocks the building of the bacterial cell wall, so the cell bursts and dies. That makes penicillin bactericidal, so Statement I is false.
- Remember the lists. NCERT lists penicillin, aminoglycosides and ofloxacin as bactericidal. Erythromycin, tetracycline and chloramphenicol are bacteriostatic.
- Statement II. The structure shows a four-membered β-lactam ring (with its C=O next to N) fused to a five-membered thiazolidine ring containing S. That ring carries two CH₃ groups and a COOH, and the β-lactam ring carries an R-CO-NH⁻ side chain. This is exactly the general structure of penicillin, so Statement II is true.
- So. Statement I is incorrect and Statement II is true, which is option (b).
The idea to keep. Penicillin is bactericidal, not bacteriostatic. Recognise it by the β-lactam ring fused to a sulphur-containing thiazolidine ring, with an R-CO-NH⁻ side chain.
Answer from the NTA final answer key. Solution by PrepWiser.