Step 1: Definition:
A "victimless crime" is an illegal act involving only the perpetrator or consenting adults, with no direct complainant. Society considers it harmful.
Step 2: Option Analysis:
1. Drug Abuse: Drug use is a prime example. The user, who is the perpetrator, is primarily harmed. There's no direct victim filing a complaint, though societal costs exist.
2. Robbery: This crime has a clear, direct victim who is subjected to force or the threat thereof.
3. Cybercrime: Hacking, fraud, and identity theft have direct victims suffering financial or personal harm.
4. Communal rioting: This crime against public order directly victimizes individuals and communities.
Step 3: Conclusion:
Drug abuse fits the victimless crime definition, lacking an immediate, direct external victim.