The correct answer is Lord Chelmsford .

The Rowlatt Act was a law passed by the British colonial government in India in 1919. It allowed the government to arrest and detain people without trial and was widely opposed by Indians, who saw it as a violation of their civil liberties and an attempt to suppress their growing movement for independence.

At the time of the passing of the Rowlatt Act, Lord Chelmsford was the Viceroy of India. He served as the Viceroy from 1916 to 1921 and was appointed by the British government to oversee the administration of India on behalf of the British monarch.

Lord Chelmsford played a key role in the passage of the Rowlatt Act, as he was the one who signed the Act into law. However, it should be noted that the Act was actually drafted by Sir Sidney Rowlatt, a British jurist who had been appointed to investigate revolutionary activities in India.

The passage of the Rowlatt Act was a major turning point in India’s struggle for independence and sparked widespread protests and civil disobedience across the country. The Act was eventually repealed in 1922, but the events surrounding its passage had a lasting impact on Indian politics and society.

In conclusion, Lord Chelmsford was the Viceroy of India when the Rowlatt Act was passed. While he played a key role in signing the Act into law, it was actually drafted by Sir Sidney Rowlatt, a British jurist appointed to investigate revolutionary activities in India.