Answer: The complex sentence of the compound sentence is 'I have a big box, where I keep all my odds and ends in it.'
Step-by-step explanation:
Compound sentences are the ones which have two independent clause. Complex sentences on the other hand have one dependent, and one independent clause.
The sentences ‘I have a big box, and I keep all my odds and ends in it’ is a compound sentence because it has two independent causes. If we have to rewrite this sentence as a complex sentence, it would be ‘I have a big box, where I keep all my odds and ends in it.’ Here the independent clause is ‘I have a big box.’ Whereas the dependent clause is ‘where I keep all my odds and ends in it’ which is dependent of the former line.