For her science project, Paula wants to determine if the growth of bacteria in standing rainwater changes over time. She collects rainwater and distributes it evenly in 6 jars and places them all indoors in a spot that does not receive a lot of sunlight to limit evaporation. Using a bacteria testing kit, she measures the bacteria in the water in the first jar on the 5th day, second jar on the 7th day, third jar on the 9th day, fourth jar on the 14th day, fifth jar on the 20th day, and sixth jar on the 24th day. What is the independent or manipulated variable in Paula's experiment?

The correct answer is - the number of days the rainwater stands in the jars.

Explanation:

The independent variable or the manipulating variable is a variable in a research or study is the variable which affects the dependent variable or the variable that is going to measure in the study.

In the study, variables that recieves the treatment and changed in every subject are independent variables and in this study number of days the rainwater standing in various jars that might affect the growth of the bacteria in rainwater.

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explanation:

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answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.