Mahatma Gandhi`s efforts to bridge economic inequalities were primarily based on the principle of trusteeship theory. According to this theory, he believed that wealthy individuals should act as trustees and use their wealth for the welfare of the society. Gandhi proposed that the rich should voluntarily give up their excess wealth and use it in a way that benefits the less privileged sections of society. This approach aimed to address the economic disparities in a non-violent and cooperative manner. It did not involve the abolition of machinery or the establishment of village industries, although those ideas were also important aspects of Gandhi`s economic philosophy. Therefore, option 4, trusteeship theory, is the correct answer in this context.