Why will a new nail react faster in copper sulfate solution than an old, rusty nail?

There could be two reasons.

1. The iron oxide hydrate (the rust) covers the Fe of the nail, and
2. Most NEW nails are galvanized (coated with Zn metal) and the Zn metal is higher in the activity series than Fe.
It isn't easy to be more specific because the question is so open ended.