Explanation:

- The minimum reserve system in India was introduced to maintain a reserve to secure the country's currency.

- It requires the Reserve Bank of India (RBI) to keep a minimum reserve of gold and foreign securities.

- Option 1: 1947

- The year of India's independence. Major economic changes were underway, but the minimum reserve system was not introduced this year.

- Option 2: 1948

- The RBI was already managing currency matters, but the minimum reserve system was not yet applied.

- Option 3: 1951

- This year is marked by the beginning of planned economic development in India, not the introduction of the minimum reserve.

- Option 4: 1957

- This is the correct answer. The minimum reserve system started in this year, to stabilize the currency and boost trust in the Indian economy.

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