Fleming discovered penicillin in 1928.

Penicillin was discovered in 1928 by Fleming.
Explanation: The sentence can be rewritten in passive because "penicillin" is the object of the action "discovered."

Everyone in the class arrived on time yesterday.

X
Explanation: The sentence can't be rewritten in the passive voice because "everyone" is the subject performing the action (arriving), and there is no direct object to become the subject in the passive form.

A helicopter rescued the six survivors from the water.

The six survivors were rescued from the water by a helicopter.
Explanation: "The six survivors" is the object receiving the action, so it can be made the subject in the passive construction.

The president congratulated the winner of the race.

The winner of the race was congratulated by the president.
Explanation: "The winner of the race" is the object receiving the action, so it can be made the subject in the passive voice.

Two prisoners escaped from the jail yesterday evening.

X
Explanation: This sentence can't be rewritten in the passive voice because the action ("escaped") is intransitive; there's no object that receives the action.

A policewoman found the two missing children in a local park.

The two missing children were found in a local park by a policewoman.
Explanation: "The two missing children" is the object receiving the action of being found, so it can become the subject in the passive construction.

They will publish her new book next year.

Her new book will be published next year.
Explanation: "Her new book" is the object receiving the action, so it can be the subject in the passive voice.

Suddenly a strange red light appeared in the sky.

X
Explanation: The verb "appeared" is intransitive (it doesn't take a direct object), so it can't be rewritten in the passive voice.