The correct option is A Guru Gobind Singh
From 1699, Guru Gobind Singh waged constant war against the armies of Aurangzeb and hill rajas. After Aurangzeb's death, he joined Bahadur Shah's camp as a noble of the rank of 5000 zat and 5000 sawar and accompanied him to Deccan where he was treacherously murdered by one of his Pathan employees. Hence, Option A is correct. Among the rest, Guru Har Kishan was the youngest guru who died before he was eight. Guru Hargobind formed the Khalsas, the militant group of Sikhs, Guru Tegh Bahadur was beheaded by Aurangzeb for refusing to convert to Islam. Hence, these are incorrect.