Which of the following is true about the variables in an experiment? A.

All variables should be kept the same.

B.

All variables should change.

C.

One variable should be kept the same and at least two variables should change.

D.

One variable should change and the others should be kept the same
(middle school)

D.  One variable should change and the others should be kept the same

Explanation:

Variable in an experiment are defined as the things that changes. There are three variables in an experiment: dependent, independent, and controlled.

Independent variable is defined as the variable which is changed by researcher during an experiment and it influence the dependent variable to be changed. Controlled variables are required to be constant in an experiment and observe them carefully.

In an experiment, it is important to change only one variable that is independent variable because changing other variables can make the result confusing and if only one variable will be changed, it would be easy to observe changes in other variables.

Hence, the correct answer is "D.  One variable should change and the others should be kept the same".

alkaline metals are lithium, sodium, rubidium, potassium, cesium and francium.

alkali metals have electronegativity from 0.7 to 1, lowest in periodic table of elements, which means that alkali metals (i group in periodic table) has positive oxidation number in compounds.

electronegativity is a chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.

alkaline metals (far left in main group) have lowest ionizations energy and easy remove valence electrons,

for example, potassium is the alkali metal and has a single valence electron in the outer electron shell.

electron configuration of potassium is: ₁₉k 1s²2s²2p⁶3s²3p⁶4s¹.

they can not exist alone in nature, because they are very reactive.