The Viceroy of India at the time of Gandhiji`s Dandi march was Lord Irwin.

Option 1: Lord Irwin is the correct answer. He served as the Viceroy of India from 1926 to 1931. During his tenure, he played a significant role in negotiating with and eventually reaching an agreement with Gandhiji during the Salt Satyagraha or the Dandi march in 1930.

Option 2: Lord Linlithgow was the Viceroy of India during World War II, from 1936 to 1944. This was after the time of Gandhiji`s Dandi march.

Option 3: Lord Reading served as the Viceroy of India from 1921 to 1926, before Gandhiji`s Dandi march.

Option 4: Lord Willingdon served as the Viceroy of India from 1931 to 1936, after Gandhiji`s Dandi march.

Therefore, the correct answer is option 1, Lord Irwin. He was the Viceroy of India at the time of Gandhiji`s Dandi march in 1930.