improtes the statement or answers the question. 1. Haircoloring products that change color gradually by progressive buildup and exposure to air contain __ . a. metallic salts b. dye precursors c. blending salts d. mineral crystals

## Step 1<br />The problem is asking us to identify the type of substance that is used in hair coloring products that change color gradually due to progressive buildup and exposure to air. The options provided are metallic salts, dye precursors, blending salts, and mineral crystals.<br /><br />## Step 2<br />Metallic salts are known to change color when exposed to air due to oxidation. This is a chemical reaction where a substance gains oxygen. This property makes metallic salts suitable for hair coloring products that change color gradually.<br /><br />## Step 3<br />Dye precursors, blending salts, and mineral crystals do not have the same property of changing color upon exposure to air. Therefore, they are not the correct answer.