Final answer:
Gold was known to mankind thousands of years ago due to its unreactive nature, while sodium was only discovered in the 1800s because it is highly reactive.
Step-by-step explanation:
Gold was known to mankind thousands of years ago because it is an unreactive material that exists in its elemental state in many places. Gold was known to mankind thousands of years ago due to its unreactive nature, while sodium was only discovered in the 1800s because it is highly reactive. This made it easier for ancient civilizations to find and use gold for various purposes, such as jewelry and decorative items.
On the other hand, sodium was only discovered in the 1800s because it is a highly reactive element that is not found in its pure form in nature. It required advancements in scientific methods and technology for chemists to isolate and study sodium.