The Basic/Key Industries (Public-cum-Private Sector) category in the Industrial Policy of 1956 included industries like coal, iron & steel, aircraft manufacturing, ship-building, manufacture of telephone, telegraph & wireless apparatus, and mineral oil.

The correct answer is option 'D' - Basic/Key Industries (Public-cum-Private Sector).

Explanation:
The Industrial Policy of 1956 was formulated by the Government of India with the aim of promoting industrial development and economic growth in the country. This policy categorized industries into different groups based on their importance and role in the country's economy.

The category designated as "Key Industries" or "Basic Industries" was considered crucial for the overall industrial development of the country. These industries were given special attention and priority in terms of government support, investment, and regulation.

Key Industries (Public-cum-Private Sector):
Under the Industrial Policy of 1956, the Basic/Key Industries category included industries that were considered strategically important for the nation's economic growth. These industries were characterized by significant capital requirements, long gestation periods, and high social returns. They were deemed essential for the development of other industries and had a multiplier effect on the economy.

Examples of Basic/Key Industries included steel, coal, iron, petroleum, and heavy machinery. These industries were crucial for infrastructural development and provided inputs to various other sectors. The government recognized that the private sector alone may not be able to adequately invest in and develop these industries due to their capital-intensive nature and long-term gestation periods. Therefore, the policy allowed for a combination of public and private sector participation in these industries.

By designating these industries as Basic/Key Industries, the government aimed to ensure their sustained growth and development by providing financial support, infrastructure, and regulatory frameworks. This approach was intended to create a strong industrial base in the country, promote self-sufficiency, and reduce dependence on imports.

The Industrial Policy of 1956 played a significant role in shaping India's industrial landscape and laid the foundation for the country's industrial development in subsequent years. The categorization of industries into Basic/Key Industries highlighted the government's commitment to promoting economic growth and achieving industrialization through a planned and regulated approach.