A biological agent with antiviral property is

1. Analyze the question The question asks for a biological agent that has antiviral properties, meaning something produced by living organisms that fights viruses.

2. Explain the concept When a cell is infected by a virus, it releases signalling proteins called interferons. These proteins warn neighbouring cells and trigger them to produce substances that block viral replication. Interferons are therefore natural antiviral agents made by the body.

3. Go through the options

• A. Interferon: A protein made by the body's own cells that interferes with viral replication. It is a biological antiviral agent, so this fits.
• B. Enzyme: Enzymes are biological catalysts that speed up reactions. They are not specifically antiviral.
• C. Antibiotic: Antibiotics such as penicillin act against bacteria, not viruses. This is a very common exam trap.
• D. Disinfectant: A chemical used on surfaces to kill germs. It is not a biological agent.

4. Answer The correct option is A. Interferon.

5. Exam tip Remember: Antibiotics → bacteria. Interferons → viruses. The name "interferon" itself hints that it interferes with viruses. If you see "antiviral" and "biological" together, think interferon.