Option 1: The statement that the All India Depressed Classes Association was formed in Nagpur with M. C. Rajah as its first elected President is correct. This provides information about the formation of the association and its initial leadership.
Option 2: The statement that the All India Depressed Classes Association was not attended by Dr. B. R. Ambedkar in 1926 is incorrect. Dr. B. R. Ambedkar was indeed present at the formation of the All India Depressed Classes Association in Nagpur in 1920.
Option 3: The statement that Ambedkar resigned from the All India Depressed Classes Association and formed his own All India Depressed Classes Congress in 1930 is correct. After a disagreement with the leadership of the association, Ambedkar resigned and went on to form his own organization, the All India Depressed Classes Congress.
Option 4: The statement that the All India Depressed Classes Association favored Ambedkar`s demand for a separate electorate for the depressed classes is correct. This was indeed one of the key demands put forward by Ambedkar, and the association supported this demand.
In conclusion, the incorrect statement is Option 2. Dr. B. R. Ambedkar did attend the