Explanation:

- Section 76 of IPC states that nothing is an offence which is done by a person who is, or who by reason of a mistake of fact and not by reason of a mistake of law in good faith believes himself to be, bound by law to do it.

- In this case, the soldier fires upon the mob by the order of his superior officer and in conformity with the law.

- Option 1 (Offence within Section 76 of IPC): This is not correct because Section 76 acts as a defence and says it is not an offence if the act is done under the compulsion of law.

- Option 2 (No offence within Section 76 of IPC): This is correct. The soldier commits no offence under Section 76 as he acts under the law's command.

- Option 3 (No offence within Section 80 of IPC): Section 80 deals with accidents in doing a lawful act, which is not directly relevant here.

- Option 4 (None of the above): Incorrect as Option 2 is correct.

The correct answer is:

Option 2: No offence within Section 76 of IPC