Is this chain solid gold or plated?

It is solid 14k rose gold, stamped 14K. That makes it more durable than gold-plated or gold-filled chains, which can wear through to the base metal.

What size pendant can it hold?

At 0.5 mm wide and about 0.8 grams, it suits small, light pendants. A heavy or large pendant can stretch or break links this thin.

What kind of clasp does it have?

It has a spring ring clasp. It is compact and sits flat, but it takes more care to open and close than a lobster clasp.

Will a 0.5 mm chain break easily?

Thin chains like this are more prone to kinking and snapping than thicker ones, especially if pulled. Treat it gently and avoid catching it on clothing.

Can I wear it in the shower or to swim?

14k gold resists tarnish, but chlorine, salt water and soap can dull it over time and weaken thin links. Taking it off before swimming or showering helps it last.