Describe how you will tell everyone that Mr. Akhil opened the gate in passive voice.

Correct option is A

Active Voice: In Active voice the subject is the one doing the action.
Passive Voice: In Passive voice the subject is the recipient of the action.
To convert active voice into passive voice the object becomes the subject and the subject becomes the object.
For Simple Past Tense as given in the question the structure for changing a sentence from active to passive and vice versa is:
(Active voice) Subject + V2+ object.
(Passive voice) Object+ was/were + V3+ by + subject.