What does the process of disinvestment in public sector undertakings primarily entail?

The correct option is Diluting the state's equity stake in public sector enterprises.

Understanding Disinvestment:
Disinvestment (or divestment) in Public Sector Undertakings (PSUs) refers to the process by which the government sells or liquidates a portion or the entirety of its equity stake (shares) in state-owned enterprises to private investors, financial institutions, or the general public.
The primary objectives of disinvestment include reducing the government's fiscal burden, raising capital for public welfare and infrastructure development, improving corporate governance, and encouraging market efficiency and competition.

Step-by-Step Evaluation of Options:
1. Bringing private corporations under government control: This process is known as nationalization, which is the direct opposite of disinvestment.
2. Shutting down chronically unprofitable state entities: This describes closure or liquidation, whereas disinvestment involves transferring ownership of equity/assets while the enterprise generally continues operation.
3. Expanding financial support and state subsidies: This represents recapitalization or budgetary support, which increases government investment rather than selling equity.
4. Diluting the state's equity stake in public sector enterprises: This accurately describes disinvestment, as selling government shares reduces (dilutes) the state's overall percentage of ownership in the PSU.

Thus, disinvestment primarily entails diluting the government's equity stake in public sector enterprises.