For the first question regarding the key characteristic of primary colors, the correct response is:
they are represented in most color wheels.
Primary colors are typically the foundation for creating other colors and are a key component of color theory as represented in color wheels.
For the second question about the color model Finn is using while making a design piece on his computer, the correct response is:
additive.
The additive color model is used in digital displays, where colors are created by adding light of different wavelengths (such as red, green, and blue).