Both hollow and solid gold jewelry are made from the same material, so you can’t tell if a piece of jewelry is solid or hollow gold just by looking at it. If you’re looking at two gold chains or a set of bracelets of the same metal quality, you won’t be able to tell which is solid gold and which is hollow.
Hollow gold jewelry means there’s empty space inside it, while solid gold jewelry is completely solid throughout. They’re both made of 100% real gold, but hollow gold jewelry requires less gold to produce the same piece of jewelry made of solid gold.