In an experiment, shara feeds her rat different brands of rat food (brands x, y, and z) each for 2 weeks and weighs the rat over several days during the period of each diet. What is the independent variable

The variables are defined as the factors in an experiment, which are liable to change. The variable can be dependent or independent. The Independent variable is a variable, which is unaffected by the changes in the other variables.

In this case, the brand of the food Shara feeds to the rats is independent factor, but it is changes in the system, so, it is an independent variable.

The effect on the weight of the rat is dependent on the brand of food they are consuming. So, the weight of rats is dependent variable.