Explanation:

- Zinc oxide:

- A pigment.

- Provides opacity and whiteness.

- Used in paints and cosmetics.

- Chalk:

- Natural form of calcium carbonate.

- Used as a white pigment.

- Common in school chalkboards.

- White lead:

- Traditional white pigment.

- Historically used in paints.

- Now replaced due to toxicity concerns.

- Silica:

- Mainly used as a filler.

- Provides structure in paints and coatings.

- Not typically used as a pigment.

Silica is not a pigment.