Explanation:

Among the given options, Khusro Bagh is not a historical monument of Lucknow; it is a large walled garden complex located in Prayagraj (formerly Allahabad), Uttar Pradesh, containing the tombs of Khusrau Mirza (Jahangir's eldest son), Shah Begum, and Princess Sultan Nithar Begum. Options (1) Rumi Darwaza, (3) Chota Imambara, and (4) Jama Masjid are all prominent historical monuments situated in Lucknow. Rumi Darwaza is an iconic gateway, Chota Imambara is a significant Shia Muslim congregation hall, and Lucknow has its own historic Jama Masjid. Thus, Khusro Bagh is the outlier by location.