The correct option is
B Work hard and win the prize.
There are three moods in English:A verb which makes a statement of fact or asks a question or expresses a supposition which is assumed as a fact is in the indicative mood.
A verb which expresses an instruction, a command, a request or a prayer, is in the imperative mood.
A verb which expresses a wish/hope/ desire/ resolution is in the Subjective mood. They include verbs like wish, hope, suggest, ask, demand, recommend, insist, advise, propose, etc and are mostly followed by the word, "that". It also states a condition/wish which is contrary to the fact. Example: "I wish that I were a millionaire".
Option A: The phrase, "Work hard" advises/ instructs the listener. Hence, this is in the imperative mood. Option A is correct.
Option B: The phrase, "In case you work hard", assumes the fact that you do and states the result (you can win the prize). Hence, it is in the indicative mood. Option B is incorrect.
Option C: The phrase, "Can I work hard and thereby win the prize" communicates a question. Hence, this is in indicative mood (more specifically also referred to as interrogative mood).
Option D: The phrase, "I wish I can work hard" is in subjunctive mood as there is a wish expressed. Hence this is not the correct answer.