Katie wants to make ball-and-stick models of the four macromolecules. She has colored balls for each of the elements in these molecules, including the following.

red: hydrogen

black: carbon

purple: oxygen

green: nitrogen

In which macromolecule will she use the black, red, and purple balls in a ratio of 1:2:1

Katie will use the black, red and purple balls in a ratio 1:2:1 for carbohydrate molecules.

There are four macro molecules in existence, these are carbohydrates, proteins, fat and oil and nucleic acids. All these molecules has carbon in their compounds. The carbohydrate is made up of the elements carbon, hydrogen and oxygen in the ratio 1: 2: 1, thus, the molecular formula of carbohydrate is C6H12O6.

The answer is carbohydrate. The carbohydrate has the ratio of C:H:O=1:2:1. In nuclei acid and protein, there is nitrogen exists. And for fatty acids, the ratio is not constant.