Following is the question on active-passive voice transformation from an exercise. Which option will be correct out of (1) and (3) and please explain the reasoning behind. I opted for (3) but the answer given is (1).
Comparing sentences (1) and (3) (the ones you asked about):
(1) I couldn't be moved to the hospital and was operated on at home by the doctor.
(3) I couldn't be moved to the hospital and I was operated at home by the doctor.
The extra "I" is optional and irrelevant.
The reason that sentence (1) is correct is that it includes the word "on", which sentence (3) omits.
"The doctor operated on me" becomes (in the passive) "I was operated on (by the doctor)".
"The technician operated the computer" becomes "The computer was operated (by the technician)".
In "the doctor operated on me", the verb phrase is "operate on", not just "operate". When you form the passive, you can't omit the preposition.