The correct option is
B He was rewarded for his courage.
A simple sentence has only one subject and predicate. It has a finite verb with a completed thought. A compound sentence has at least two parts (also referred to as a clause). Each part has its own subject and predicate and makes good sense by itself. Hence each clause is independent of the other and called the main clause or independent clause. The main clauses are connected using a co-ordinating conjunction (for, and, nor, but, or, yet, so).A complex sentence has at least one main clause (which is an independent clause) and one or more dependent clauses, connected using a subordinate conjunction. The dependent clause cannot stand by itself and make good sense. It depends on the main clause.
Option A: The two clauses viz (i) "He was courageous" and (ii) "he was rewarded", can stand independently and make good sense. They are independent clausesconnected using the co-ordinating conjunction-"and". Hence, this is a compound sentence and this answer is incorrect.
Option B: This sentence has only one clause i.e., "He was rewarded". It has only a single subject ("He") and predicate ("was rewarded"). The words, "for his courage" is a phrase and not a clause. Hence, this is a simple sentence and this option is correct.
Option C: The word, "because" is a subordinating conjunction which connects dependent and independent clauses. The clause, "He was rewarded" is an independent clause. The clause, "because he was courageous" cannot stand by itself and make good sense. It is a dependent clause. Hence, this is a complex sentence and this option is incorrect.
Option D: The word, "though" is a subordinating conjunction which connects dependent and independent clauses. The clause, "He was not rewarded" is an independent clause. The clause, "though he was courageous" cannot stand by itself and make good sense. It is a dependent clause. Hence, this is a complex sentence and this option is incorrect.