Is this solid gold or gold plated?

It is sterling silver with a 14K gold plate over it, not solid gold. The silver core keeps it affordable, but the gold layer is a finish, not the metal itself.

Will the gold plating wear off?

Plating wears fastest where the chain rubs: the clasp, the jump ring and the links that move most. Taking it off before showering, swimming or applying perfume slows that down.

What length is it and where does it sit?

It is 18 inches, which generally falls at the collarbone on most adults. That length works alone or as the base layer under a shorter choker.

Can I wear a pendant on it?

Light pendants are fine. Box chains are less flexible than cable or curb chains, so a heavy pendant can strain the links and the clasp.

How do I keep it from tarnishing?

Keep it dry, wipe it after wearing and store it in a sealed bag away from humidity. Sterling silver tarnishes naturally, and plated pieces should not be polished with abrasive cloths.

Is it good for daily wear?

It handles daily wear, but the plating will show age sooner than solid gold. If you want a chain to wear constantly for years, solid gold holds up better.