Which of these is a pure substance
bread
seawater
table salt
garden soil

Table salt.

Explanation:

A pure substance has a constant composition and cannot be separated into simpler substances by physical means. There are two types of pure substances: elements and compounds. Elements are pure substances made up of only l type of atom.

Bread is a mixture of substances. Seawater includes water and salt, which is more than one substance. Garden soil had has many types of substances, especially enhanced types like potting soil with plant feed. So your only answer is table salt.

Hope this helps!

the titanic would be the correct answer