The video explains that substances have a definite chemical composition and distinct properties. Each element and pure compound is a unique substance, while mixtures like seawater consist of multiple substances rather than being a single substance.

What characteristic defines a substance?

• It cannot be a compound.

• It is always a mixture.

• It has a definite chemical composition.

• It has a variable composition.

Which of the following is considered a distinct substance?

• A pure element like gold

• A glass of seawater

• A mixture of sand and salt

• A salad

Which of the following is NOT a characteristic of a pure compound?

• It is a unique substance.

• It is a mixture of different substances.

• It has distinct properties.

• It has a definite chemical composition.

How is seawater classified in terms of substances?

• As a pure compound

• As a mixture of substances

• As a distinct element

• As a single substance

What is the main difference between a substance and a mixture?

• Neither has a definite composition.

• Both have definite compositions.

• A mixture has a definite composition, while a substance does not.

• A substance has a definite composition, while a mixture does not.