In this question on Active and Passive voice, you must choose the passive form that best expresses the meaning of the sentence "Ram was singing a beautiful song for his mother."

Introduction / Context:
This question tests your understanding of transforming sentences from Active voice to Passive voice in English grammar. The given sentence is in the past continuous tense and describes an ongoing action in the past. To get full marks, you must convert it into a passive structure that maintains the tense, the meaning, and the focus of the sentence correctly.

Given Data / Assumptions:
- Active sentence: "Ram was singing a beautiful song for his mother."
- Subject in the active voice: Ram.
- Object in the active voice: a beautiful song.
- The action is in past continuous tense: "was singing".
- Four passive voice options are given, and exactly one correctly preserves tense and meaning.

Concept / Approach:
To convert a sentence from Active to Passive voice, the object of the active sentence becomes the subject of the passive sentence. The verb form is changed using a form of "be" plus the past participle of the main verb, and the original subject is usually introduced with "by". For continuous tenses, the structure "was being" or "were being" plus past participle is used. Here, "was singing" must become "was being sung" in the passive form.

Step-by-Step Solution:
Step 1: Identify the object "a beautiful song" and make it the new subject in the passive sentence. Step 2: Recognise that the tense is past continuous, so the passive auxiliary must be "was being". Step 3: The past participle of "sing" is "sung", not "sang". Step 4: Insert "by Ram" to show who performed the action. Step 5: Keep the phrase "for his mother" at the end to preserve the meaning.

Verification / Alternative check:
Constructing the passive voice step by step gives: "A beautiful song" (object becomes subject) + "was being sung" (correct past continuous passive form) + "by Ram" (agent) + "for his mother" (beneficiary). This exactly matches option A: "A beautiful song was being sung by Ram for his mother." The tense, agent, and purpose remain unchanged, so this option is correct.

Why Other Options Are Wrong:
Option B, "A beautiful song was sang by Ram for his mother", is wrong because "sang" is the simple past form, not the past participle, and there is no "being", so the continuous aspect is lost. Option C, "A beautiful song was sung by Ram for his mother", uses the correct participle but expresses simple past tense, not past continuous. Option D, "A beautiful song was sung for his mother by Ram", has the same problem as option C; it is simple past and does not reflect the ongoing nature of the action.

Common Pitfalls:
Students often forget to include "being" when changing continuous tenses to passive voice, where it is essential to show the ongoing nature of the action. Another frequent mistake is using the wrong verb form, such as "sang" instead of "sung". To avoid these errors, always identify the tense first, then apply the correct passive structure: subject plus appropriate form of "be" plus past participle, adding "being" for continuous tenses and "been" for perfect tenses.

Final Answer:
The correct passive voice form is "A beautiful song was being sung by Ram for his mother."