Which of the following options is the most suitable conversion of the following sentence into Passive Voice?

Somebody is sure to discover the missing documents.

Correct Answer: The missing documents are sure to be discovered.

Detailed Explanation:
To convert a sentence containing an infinitive structure from Active Voice to Passive Voice, we follow these step-by-step grammatical rules:

Step 1: Identify the components of the active sentence
• Subject: Somebody (an indefinite pronoun)
• Predicate construction: is sure to
• Active Infinitive: discover (to + V1)
• Object: the missing documents

Step 2: Make the object the new subject with proper verb agreement
• The object "the missing documents" becomes the subject of the passive sentence.
• Since "the missing documents" is plural, the auxiliary verb changes from singular (is) to plural (are): "The missing documents are sure..."

Step 3: Convert the active infinitive into a passive infinitive
• Active infinitive form: to + V1 (to discover)
• Passive infinitive form: to + be + V3 (Past Participle) (to be discovered)

Step 4: Omit vague or indefinite agents
• Indefinite pronouns such as somebody, someone, or people serving as the subject in an active sentence are omitted in the passive voice because the agent performing the action is unknown, general, or unnecessary to mention.

Combining all the steps gives the correct passive sentence:
"The missing documents are sure to be discovered."