Four groups of rats are first massed and then fed identical diets except for 2 points the amount of vitamin A they receive. Each group gets a different amount.
After 3 weeks on the diet, the rats' masses are measured again to see if
there has been a decrease. Name the independent and dependent
variable. *

The independent variable is the diet while the dependent  variable is rats'

mass.

An independent variable in an experiment usually undergoes some changes

in order to measure the impact they have on the dependent variable. A

dependent variable as the name implies relies on changes in the

independent variable to measure it.

In this scenario, the measured changes in diet exerts a positive or negative  

effect on the mass of the rats which is why the diet is the independent

variable and the dependent variable is the rats' mass.

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The independent variable: Diet

The dependent  variable: Rats' mass

Explanation:

The independent variable in an experiment is defined as the variable that can be changed or controlled to find its impact on the dependent variable. The dependent variable is defined as the variable that is influenced by the change in the independent variable.

In the given experiment diet is the independent variable as its quantity is changing in different weeks and affecting the mass of rats' and mass of rats' is the  dependent  variable as it is measured by the influence of diet.

Hence, the correct answer is:

The independent variable: Diet

The dependent  variable: Rats' mass