In the following question, a sentence has been given in Active/Passive voice. Out of the four alternatives suggested, select the one which best expresses the same sentence in Passive/Active voice. He mailed his application for a new job.

Introduction / Context:
This question checks the ability to transform a sentence from active voice to passive voice while preserving tense and meaning. The original sentence is He mailed his application for a new job. We must find the passive version that correctly changes the focus from the doer of the action, he, to the receiver of the action, the application. Voice change questions are common in grammar tests because they require understanding of tense, object, and subject relationships.

Given Data / Assumptions:

• The active sentence is in simple past tense, indicated by mailed.
• The subject is He.
• The object is his application for a new job.
• In passive voice, the object should become the subject of the new sentence.
• The tense must remain simple past in the passive form.

Concept / Approach:
To convert a simple past tense active sentence into passive voice, the pattern is: Subject plus mailed plus object becomes Object plus was or were plus mailed plus by plus subject. Thus, His application for a new job (object) must move to the subject position, and we must use was mailed because application is singular. The agent can optionally be expressed using by him. The key is to keep the verb mailed as past participle and use the correct auxiliary was for simple past passive.

Step-by-Step Solution:
Step 1: Identify the object of the active sentence, which is his application for a new job. Step 2: Place this phrase in the subject position in the passive sentence. Step 3: Because the active verb mailed is in simple past, choose the simple past form of be, which is was for a singular subject. Step 4: Follow was with the past participle mailed to form was mailed. Step 5: Add the preposition by and then the original subject him to show the agent, giving by him. Step 6: The full passive sentence becomes The application for a new job was mailed by him. Step 7: Compare this with the given options and note that Option B matches exactly.

Verification / Alternative check:
Check each alternative quickly. Option A uses is mailed, which is present tense, not simple past, so it changes the time of the action. Option B keeps the tense in the past with was mailed and includes by him, preserving meaning. Option C, He is the mailer of the application for a new job, changes both structure and focus and is not a direct passive transformation. Option D, He was the mailer, again does not follow the standard passive voice pattern with was mailed. Option E, His application for a new job was mailed, is grammatically correct but omits the agent by him; while acceptable as a passive, the question typically prefers the full agent expressing option given, which is Option B.

Why Other Options Are Wrong:
The application for a new job is mailed by him is wrong because the verb is in the present tense is mailed, which does not match the original past tense mailed. He is the mailer of the application for a new job uses a noun form mailer and changes the structure entirely, so it is not a straightforward voice change. He was the mailer of the application for a new job does the same in past tense but still does not follow the expected passive construction. His application for a new job was mailed, although grammatically fine, omits the explicit agent by him that the exam usually expects when offering direct active passive pairs side by side.

Common Pitfalls:
Learners sometimes forget to maintain the tense when changing from active to passive, resulting in errors like is mailed in place of was mailed. Another common mistake is to use an incorrect auxiliary such as has mailed or is mailing, which changes the aspect. Some candidates also struggle with placing the object correctly in the subject position. Practising with a simple pattern Subject plus verb plus object becomes Object plus form of be plus past participle plus by plus subject helps internalise the process.

Final Answer:
The correct passive voice form is The application for a new job was mailed by him.