Fill in the blank in the following sentence with the most appropriate…

The correct answer is Option (4) → delivered

Past participle phrase (reduced relative clause):

• A clause like "which was delivered by ..." can be shortened by dropping which was; the past participle alone then describes the noun.
• This sentence: "the class lecture, (which was) delivered by Professor Sinha" describes the lecture, which the professor gave earlier.
• Complete sentence: She sent a recording of the class lecture, delivered by Professor Sinha.
  Example: We read a speech delivered by Swami Vivekananda in Chicago.

Why the Other Options are Incorrect?

Option 1: was delivered — Incorrect. A finite verb like "was delivered" needs which before it; without it the sentence has two main verbs.
Example: The lecture was delivered in the main hall.

Option 2: is delivered — Incorrect. It is a finite present form; it also needs "which" and does not match the past "sent".
Example: The newspaper is delivered every morning.

Option 3: being delivered — Incorrect. Being delivered shows an action in progress; the lecture was already over when its recording was sent.
Example: The speech being delivered now is broadcast live.

Contrast: delivered describes a finished action; being delivered describes an action still going on.