Q. What is an antibiotic -

Explanation by: Official MCQ Buddy

Antibiotics are substances naturally produced by microorganisms (such as bacteria and fungi) that inhibit or kill other microorganisms, primarily bacteria.
Option C ("A synthetic compound inhibiting the growth of bacteria") is incorrect because antibiotics are not necessarily synthetic. While some antibiotics are modified synthetically (semi-synthetic antibiotics), the original antibiotics (like penicillin) are naturally produced by microbes.
Thus, option B is the most accurate because it correctly states that antibiotics are produced by living organisms and inhibit the growth of other organisms.