Option 1: Lord Dalhousie. Lord Dalhousie was the Governor-General of India from 1848 to 1856. He implemented several policies that were seen as oppressive and contributed to discontent among Indians, which eventually led to the Revolt of 1857. However, there is no evidence to suggest that Lord Dalhousie explicitly admitted the revolt as a national revolt.

Option 2: Lord Canning. Lord Canning was the Governor-General of India during the time of the Revolt of 1857. While he recognized the gravity of the situation and implemented measures to suppress the revolt, there is no information to suggest that he explicitly admitted it as a national revolt.

Option 3: Lord Ellenborough. Lord Ellenborough was the Governor-General of India from 1841 to 1844 and was not in office during the time of the Revolt of 1857. Therefore, he cannot be considered for this question.

Option 4: Disraeli. Benjamin Disraeli was a British politician and served as Prime Minister from 1874 to 1880. There is no documented evidence to suggest that Disraeli admitted the Revolt of 1857 as a national revolt.

Therefore, the correct answer is Option