Answer : Hypothesis.
Explanation : Hypothesis is defined as the supposition or proposed explanation which can be made on the basis of limited available evidence as a starting point for further investigation. Here, in this question the proposed explanation for the changing colors of the sky is an example of a hypothesis.
A hypothesis has to be supported with scientific experiments which are reproducible by several experiments and test results have to be valid to be called as a scientific theory.
The accepted model of an atom was made by Schrodinger, which is known as the quantum mechanical model. Unlike Bohr's model, electrons are represented as a cloud and not small balls orbiting the nucleus. There is no define path of electrons in Schrodinger's model, but it can predict the odds of where an electron is located.
The answer to your question is then Electrons form a cloud around the nucleus.
The question that will best help the student to classify the material is; "is the material malleable or ductile?"
Generally, materials can be classified as metals or non metals. There are properties that are particular to metals and there are properties that are particular to nonmetals and these properties can be used to identify each one of the materials.
The question that will best help the student to classify the material is; "is the material malleable or ductile?" These metallic properties.
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Missing parts;
A student is trying to classify an unidentified, solid gray material as a metal or a nonmetal. Which question will best help the student classify the material? A. Is the material malleable or ductile? B. Does the material feel hard to the touch? C. Will the material float in water? D. Does the material feel rough or smooth?