Elimination by mechanism:
Cash Reserve Ratio is a proportion of deposits banks must hold with the central bank, it is a reserve requirement, not a lending rate, so it does not match discounting securities. Open Market Operations involve the central bank buying or selling government securities in the market, not lending against them through discounting. Cash Deposit Ratio is not a recognized monetary policy instrument at all.
The only instrument that specifically describes the central bank extending financial accommodation to commercial banks by discounting government or first-class securities is the Bank Rate (also called the Discount Rate), this is its textbook definition.
Hence, option (1) is correct.