Which of the following below is a compound?

• H₃

• S₄

• O

• NO₂

Answer explanation

A compound consists of two or more different elements chemically bonded. NO₂ (nitrogen dioxide) is a compound made of nitrogen and oxygen. In contrast, H₃, S₄, and O are not compounds as they consist of either one element or identical atoms.

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Which of the following below is an element?

• Ca

• OH

• BP

• C₃

Answer explanation

The correct answer is Ca, which stands for calcium, a chemical element. OH is a hydroxide ion, BP is not a recognized element, and C₃ does not represent a single element but rather a molecular formula.

Which of the following is not a molecule?

• CaCl

• Rh

• C₃

• Bi₃

Answer explanation

Rh (rhodium) is a chemical element and a metal, not a molecule. Molecules are formed from two or more atoms bonded together, while Rh exists as individual atoms.

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The two smaller circles in the image to the right represent element A, and the circle in the middle represents another element, element B. What conclusion can you draw?

• This image is an example of a single element

• This image is a molecule because the same elements have combined together

• This image is a compound because different elements have combined with each other

• This image is an example of three different elements

Answer explanation

The image shows two smaller circles representing element A and a larger circle for element B. Since different elements are combined, this represents a compound, not a single element or a molecule of the same elements.

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The reaction below shows two pure substances chemically combining. How would you describe the reactants?

• SO₂ is an element and O₂ is a compound.

• SO₂ is a compound and O₂ is a molecule.

• Both SO₂ and O₂ are compounds.

• SO₂ is a mixture and O₂ is a molecule.

Answer explanation

SO₂ is a compound made of sulfur and oxygen atoms, while O₂ is a molecule consisting of two oxygen atoms. Therefore, the correct description is that SO₂ is a compound and O₂ is a molecule.

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Water (H₂O) is best classified as a

• Element

• Compound

• Atom

• Mixture

Answer explanation

Water (H₂O) is a compound because it consists of two different elements, hydrogen and oxygen, chemically bonded together. It is not an element, atom, or mixture.

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How many different elements are in one Hydrogen peroxide (H₂O₂) molecule?

• 2

• 4

• 8

• 22

Answer explanation

A hydrogen peroxide (H₂O₂) molecule contains two different elements: hydrogen (H) and oxygen (O). Therefore, the correct answer is 2.

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The image shows three oxygen atoms that have bonded together to form ozone. What conclusions are you able to draw?

• Ozone is a compound because different elements have combined to form a new pure substance

• Ozone is a molecule because atoms of the same element combined to form a new pure substance

• Ozone is one element that can be found on the Periodic Table

• Ozone is an element that is a poor conductor of electricity and is very ductile

Answer explanation

Ozone consists of three oxygen atoms, making it a molecule formed from the same element. This distinguishes it from a compound, which involves different elements. Thus, the correct conclusion is that ozone is a molecule.

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How does a compound differ from a molecule?

• Compounds are only when two different elements bond together and molecules are when elements in general bond together, whether they are the same element or different elements

• Molecules are only when two different elements bond together and compounds are when elements in general bond together

• Molecules have only one atom and compounds have multiple atoms together

• Compounds have only one atom and molecules have multiple atoms together

Answer explanation

The correct choice explains that compounds consist of two different elements bonded together, while molecules can be formed by any elements, including the same ones. This distinction clarifies the definitions of both terms.

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What is the atom breakdown for the following compound: F₂W

• One atom of fluorine and two atoms of tungsten

• Two atoms of fluorine and one atom of tungsten

• One atom of fluorine and one atom of tungsten

• Two atoms of fluorine and two atoms of tungsten

Answer explanation

The formula F₂W indicates there are two fluorine (F) atoms and one tungsten (W) atom. Therefore, the correct breakdown is two atoms of fluorine and one atom of tungsten.

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