Is this sentences a compound sentence She washed the shells and dried them in sun?

No, the sentence "She washed the shells and dried them in the sun" is a complex sentence.

Here's why:

* Compound Sentence: Contains two or more independent clauses joined by a coordinating conjunction (for, and, nor, but, or, yet, so).

* Complex Sentence: Contains one independent clause and one or more dependent clauses.

In this sentence:

* Independent Clause: "She washed the shells."

* Dependent Clause: "and dried them in the sun" (this clause depends on the independent clause for its meaning).

Since it has a dependent clause, the sentence is complex.