What is one standardized variable for the following experiment?

Ten different African violet varieties were monitored to determine which varieties produced the most flowers. The plants were grown in windowsills throughout a house in self watering pots. The plants were watered with reverse osmosis water plus fertilizer.
Results:
The miniature varieties potted in 2 inch pots flowered more than the standard sized varieties plotted in 4 inch pots. Plants with blue flowers produced more flowers than plants with pink flowers.

a) variety of African violet
b) size of the pot
c) reverse osmosis water
d) location the plants were grown
e) color of flower

My guess is C because it's the factor that's kept the same in all of the treatments. Is this correct? If I'm wrong, could you please explain why?

You gave detailed data, but did not frame the question clearly. Are you looking for the independent variable?

An independent variable is the potential stimulus or cause, usually directly manipulated by the experimenter, so it could also be called a manipulative variable.

The independent variable in this situation seems to be the size of the pot. The water was given to all the plants, so it cannot account for the difference. Unless the windowsills had varying amounts of sunlight, the location cannot be considered an independent variable. However, it might be an extraneous variable.

Extraneous variables — other than the independent variable — potentially can affect the dependent variable, so they must be controlled. If possible, you try to keep them constant between the experimental and control groups.

I assume that the color of the flower would be related to the type of African violet, so that both or neither can be considered the independent variable.

I hope this helps. Thanks for asking.

I am looking for the standardized variable...

In this experiment, a standardized variable is a factor that is kept constant throughout all the treatments. It allows for a fair comparison between the different African violet varieties.

Based on the information provided, the standardized variable in this experiment is the location where the plants were grown. This is because the plants were all grown in windowsills throughout a house. Keeping the location constant ensures that environmental factors like temperature, sunlight exposure, and humidity remain consistent across all the plants, reducing their impact on the results.

Therefore, the correct answer is not C (reverse osmosis water), but D (location the plants were grown). The reverse osmosis water and other factors mentioned (variety of African violet, size of the pot, and color of flower) are the variables being tested or manipulated in the experiment.