In this English grammar question on voice, a sentence in the active voice is given in the simple future tense about corrosion. Out of the four alternatives, select the option which best expresses the same idea in the passive voice: The moist air will corrode the beam.

Introduction / Context:
This question asks you to convert a simple future active sentence into a simple future passive sentence. The original sentence "The moist air will corrode the beam" predicts that in the future, moist air will cause corrosion of a beam. In the passive voice version, "the beam" should become the subject, and the sentence must still express the same future prediction. Correct handling of future passive forms is important for both technical and general English usage.

Given Data / Assumptions:

• The tense is simple future, indicated by "will corrode".
• The subject is "The moist air".
• The object is "the beam".
• The verb "corrode" describes what moist air will do to the beam.
• The passive version must keep the future prediction and clearly show the beam as the affected item.

Concept / Approach:
In simple future tense, the passive voice is formed using "will be + past participle". The object "the beam" becomes the subject in the passive sentence. The auxiliary "will" remains, followed by "be" and the past participle "corroded". The original subject "moist air" appears after the verb phrase, usually without an article when used as a general substance, and is introduced by "by". The resulting sentence states that the beam is the thing that will experience corrosion caused by moist air in the future.

Step-by-Step Solution:
First, identify "the beam" as the object that will be promoted to subject position in the passive sentence. Second, note that the tense is simple future, so the passive auxiliary must be "will be". Third, form the passive verb phrase "will be corroded" using the past participle of "corrode". Fourth, add the agent phrase "by moist air" to indicate what will cause the corrosion. Fifth, put all parts together to obtain the full sentence "The beam will be corroded by moist air" and check that the meaning is unchanged.

Verification / Alternative check:
The passive sentence "The beam will be corroded by moist air" clearly conveys that in the future, moistened air will damage the beam. The phrase "will be corroded" matches "will corrode" in future time reference but places the beam at the centre of attention. The agent phrase "by moist air" shows the cause in a concise way. When you compare it with the original active sentence, it is obvious that the core idea remains the same, with only the grammatical structure altered.

Why Other Options Are Wrong:
Option A uses a nominal phrase "Corroding of the beam will be done", which is unnecessarily complex and unnatural, and does not reflect the simple passive form that is expected. Option B brings in "would be done" instead of "will be corroded", which changes the tense and mood. Option C is a clumsy phrase "would be under corrosion" and again moves away from the simple future passive pattern. Only option D correctly uses "will be corroded" and presents a natural, direct passive version of the original sentence.

Common Pitfalls:
Students often confuse "will be + past participle" with patterns like "would be" or "will have been", leading to tense or aspect errors. Another common issue is overusing nominalised expressions such as "corroding of the beam", which sound heavy and are not usually required in exam answers. Some learners also leave out "by" or fail to mention the agent at all, which can reduce clarity in technical statements about causes of damage. To avoid these problems, remember that simple future passive keeps "will", adds "be", and then uses the past participle, with the original object turned into the subject.

Final Answer:
The option that correctly expresses the sentence in the passive voice is: The beam will be corroded by moist air.