During British rule in India, which Viceroy was assassinated while on a visit to the Andaman Islands, making him the only Viceroy of India to be killed in office?

Introduction / Context:
The office of the Viceroy of India was the highest representative of the British Crown in the subcontinent. Although many Viceroys faced political crises and occasional violence, only one was actually assassinated while still in office. Knowing the identity of this Viceroy and the circumstances of his death is a standard factual question in modern Indian history.

Given Data / Assumptions:

- The question asks for the only Viceroy of India who was assassinated. - It mentions that the incident occurred during a visit to the Andaman Islands. - The options are Lord Harding, Lord Northbrook, Lord Ellenborough and Lord Mayo. - We assume standard timelines for Viceroys of India in the nineteenth century.

Concept / Approach:
Lord Mayo served as Viceroy of India from 1869 to 1872. During an inspection tour of the penal settlement in the Andaman Islands, he was assassinated by a convict at Port Blair in 1872. This incident is unique in the history of the viceroyalty; no other Viceroy was killed in similar circumstances. Lord Ellenborough and Lord Northbrook were earlier nineteenth century governors general and Viceroys, and Lord Hardinge refers to different incumbents who faced attacks but survived. Only Lord Mayo died as a result of an assassination while in office.

Step-by-Step Solution:
Step 1: Recall that the Andaman Islands housed a penal settlement where convicts were transported from mainland India. Step 2: Lord Mayo, as Viceroy, decided to inspect this settlement and travelled to Port Blair. Step 3: During this visit in 1872, he was stabbed by a convict and died from his wounds, becoming the only Viceroy to be assassinated while in office. Step 4: Check the other options: Lord Ellenborough and Lord Northbrook completed their terms and returned to Britain without being assassinated. Step 5: Lord Hardinge of Penshurst was injured in a bomb attack in Delhi in 1912 but survived; he was therefore not assassinated. Step 6: Conclude that Lord Mayo uniquely fits the description in the question.

Verification / Alternative check:
Chronological lists of Viceroys consistently note next to Lord Mayo's name that he was assassinated at Port Blair in 1872. Descriptions of the Andaman penal colony frequently mention this episode as a dramatic moment in its history. There is no similar annotation for any of the other Viceroys listed, which confirms that Lord Mayo was the only one killed in office.

Why Other Options Are Wrong:
Lord Harding: Usually referring to Lord Hardinge of Penshurst, who survived a bomb attack in Delhi; he was not killed.
Lord Northbrook: Served as Viceroy in the 1870s and left office normally without assassination.
Lord Ellenborough: An earlier Governor General in the 1840s, who also completed his term and returned to Britain safely.

Common Pitfalls:
Because there was a serious attack on Lord Hardinge in 1912, some students mistakenly believe he was the assassinated Viceroy. Another pitfall is to confuse different British officials who were attacked, such as district officers or governors, with the Viceroy. The key memory aid is to pair Port Blair and the Andaman penal colony with Lord Mayo as the only assassinated Viceroy.

Final Answer:
The only Viceroy of India who was assassinated in office was Lord Mayo.