The correct answer is C. Ploughing back of profits means retaining the earnings of a company for further investment. It is a way for companies to grow their business without having to raise additional capital from shareholders or debt.
Option A is incorrect because ploughing back of profits does not involve earning black money. Black money is money that is earned or obtained illegally and is not declared to the government.
Option B is incorrect because dividends not claimed by shareholders are not ploughed back into the company. They are either paid out to the shareholders or retained by the company as retained earnings.
Option D is incorrect because not paying dividends in a particular year does not necessarily mean that the company is ploughing back its profits. The company may simply be choosing not to pay dividends for strategic reasons.