Mangal Pandey was hanged on March 29, 1857, and Hazrat Mahal led the revolt at Lucknow. Nana Saheb led the revolt at Kanpur, not Bareilly. Syed Ahmad Khan wrote "Causes of the Indian Revolt". Therefore, statements 2 and 3 are correct, statement 4 is incorrect, and statement 1 is correct. Given the options, the most plausible answer that consists of undeniably correct statements is "Only 2 & 3".