Explanation:

- Option 1: Section 120

- Refers to the definition of offenses involving criminal conspiracy.

- However, does not specifically detail criminal conspiracy itself.

- Option 2: Section 120-A

- Provides the explicit definition of "criminal conspiracy" in the IPC.

- It explains the essentials required to establish a criminal conspiracy.

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- Option 3: Section 120-B

- Deals with the punishment for criminal conspiracy.

- It does not define criminal conspiracy but outlines penalties.

- Option 4: None of the above

- Incorrect as Section 120-A defines criminal conspiracy.

In summary, Section 120-A is the section that defines criminal conspiracy under the IPC.