Bank rate is the rate at which the Reserve Bank of India provides loans to scheduled commercial banks. This means that when scheduled commercial banks need to borrow money from the Reserve Bank of India, they can do so at the bank rate.

Option 1: Public Sector Undertakings. Public Sector Undertakings are government-owned companies. The bank rate does not pertain to loans provided to public sector undertakings.

Option 3: Private Corporate Sector. The bank rate does not pertain to loans provided to the private corporate sector. It specifically applies to scheduled commercial banks.

Option 4: Non-Banking Financial Institutions. The bank rate does not pertain to loans provided to non-banking financial institutions. It specifically applies to scheduled commercial banks.

Therefore, the correct answer is option 2: Scheduled Commercial Banks. The Reserve Bank of India provides loans to scheduled commercial banks at the bank rate.