Select most appropriate option to fill in the blank.The receptionist…

The correct answer is Option (1) → had arrived

Note: The given answer is as per the official NTA Answer Key. However, more than one answer is possible here: Option (1) "had arrived" and Option (2) "arrived" both make a correct sentence, as explained below.

Option 1: had arrived — Correct (Answer as per NTA).

• When two actions are in the past, the one that happened first takes the past perfect (had + past participle); the later one takes the simple past.
• After a reporting verb in the past ("informed"), the verb of the reported clause moves one step back in time.
• Clue word: "informed" (a past reporting verb), with "an hour ago" placing the arrival before the informing.
• This sentence: the applicants arrived first, and the receptionist informed the manager later, so the earlier action is "had arrived".
  Example: When we reached the hall, the show had begun.

Option 2: arrived — Can also be considered as correct. Ago marks a definite point in past time, and with "ago" English normally uses the simple past. In reported speech the simple past is often kept when the order of events is already clear, so "a number of applicants arrived an hour ago" is also correct.
Example: He told me that the parcel arrived two days ago.

Option 3: were arriving — Incorrect. The past continuous shows an action in progress; the arrival was completed before the receptionist spoke.

Option 4: have arrived — Incorrect. The present perfect is linked to the present; it cannot follow the past reporting verb "informed" or go with a past time like "an hour ago".

Complete sentence: The receptionist informed the manager that a number of applicants had arrived an hour ago.