Step 1: Understanding the Historical Event
The question asks to identify the Prime Minister of India who was in power when major commercial banks were nationalized.
Step 2: Recalling the Bank Nationalization
There were two major phases of bank nationalization in India:
First Phase (1969): On July 19, 1969, the Government of India, led by Prime Minister Indira Gandhi, nationalized the 14 largest commercial banks in the country through an ordinance. The stated objective was to have greater control over credit delivery and to align the banking sector with national development goals.
Second Phase (1980): In 1980, the government, again led by Prime Minister Indira Gandhi, nationalized an additional six banks.
Step 3: Evaluating the Options
Based on the historical facts, Indira Gandhi was the Prime Minister during both major phases of bank nationalization.
Step 4: Final Answer
Indira Gandhi was the Prime Minister who nationalized banks. Therefore, option (B) is the correct answer.