The correct answer is (b). Section 149 of the Indian Penal Code defines unlawful assembly. It states that an assembly of five or more persons is unlawful if the common object of the persons composing that assembly is to commit an offence or an act which is the common object of that assembly is an offence.
Section 34 of the Indian Penal Code deals with criminal conspiracy. It states that when a person agrees with one or more persons to commit an offence, and in pursuance of that agreement, one or more of them do an act towards the commission of that offence, all of them are guilty of the offence.
Section 146 of the Indian Penal Code deals with riot. It states that an assembly of five or more persons who, with the common object of committing an offence which is an offence punishable with death, imprisonment for life, or rigorous imprisonment for a term of two years or upwards, prepare to use force or violence to the person or property of any other person, or commit any act towards the commission of such offence, is an unlawful assembly.
The answer is (b) because Section 149 of the Indian Penal Code defines unlawful assembly.