The Indian government restricted foreign trade and foreign investment after Independence to protect domestic producers from foreign competition. Since industries were just coming up in the 1950s and 1960s, competition from imports at that stage would not have allowed these industries to develop. Therefore, only essential items like machinery, fertilisers, and petroleum were allowed to be imported.
This is a standard 2-mark question from Chapter 4 (Globalisation). Examiners look for two clear points: (1) protection of domestic/infant industries from foreign competition, and (2) the context — industries were newly developing in 1950s–60s. Avoid writing too much; two focused sentences are enough. The exact phrase "industries were just coming up" from the textbook scores well.
Source: Globalisation and the Indian Economy, Chapter 4 — Liberalisation of foreign trade and foreign investment policy