Under Section 141 IPC, an assembly of five or more persons becomes 'unlawful' if the common object of the persons composing the assembly is:

1. Section 141 IPC defines 'unlawful assembly' as an assembly of FIVE or more persons whose COMMON OBJECT is one of the five enumerated objects: (i) to overawe by criminal force or show of criminal force the Central or State Government, Parliament/Legislature, or any public servant in lawful exercise of power; (ii) to resist execution of law or legal process; (iii) to commit any mischief or criminal trespass or other offence; (iv) by force or show of force, to take or obtain possession of property; (v) by force or show of force, to compel any person to do what he is not legally bound to do or omit what he is legally entitled to do. 2. Mere assembly without one of these objects is not unlawful. 3. Knowledge of the unlawful object is essential for membership liability. 4. The number five is a minimum; if fewer, no unlawful assembly. 5. Hence option B is correct. _Source: Indian Penal Code 1860 / Code of Criminal Procedure 1973 / Indian Evidence Act 1872 (Bare Acts, indiacode.nic.in) — IPC, Section 141_