Mahatma Gandhi was against separate electorates for the Depressed Classes because 

According to Gandhi, separate electorates to the "Untouchables" would ensure their bondage

The correct answer is Option (4) → According to Gandhi, separate electorates to the "Untouchables" would ensure their bondage

At the Round Table Conference Mahatma Gandhi stated his arguments against separate electorates for the Depressed Classes:

Separate electorates to the “Untouchables” will ensure them bondage in perpetuity … Do you want the “Untouchables” to remain “Untouchables” for ever? Well, the separate electorates would perpetuate the stigma. What is needed is destruction of “Untouchability”, and when you have done it, the bar sinister, which has been imposed by an insolent “superior” class upon an “inferior” class will be destroyed. When you have destroyed the bar sinister to whom will you give the separate electorate.