Elements Molecules Compounds

The element oxygen, represented by the symbol O, is classified as

• a pure substance
• a compound
• a mixture
• a solution

Carbon (C) and hydrogen (H) are pure substances. Each is made of only one type of atom, but carbon atoms are different from hydrogen atoms. Carbon and hydrogen chemically combine to form methane (CH4).

• methane is an element and carbon and hydrogen are compounds.
• carbon, hydrogen, and methane are all elements.
• carbon, hydrogen, and methane are all compounds.
• carbon and hydrogen are elements and methane is a compound.

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What is a compound?

• an atom with more electrons than protons
• a substance in which the atoms of two or more elements are combined together
• an atom with more neutrons than protons
• a substance in which the atoms of three or more elements are combined together

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Carbon dioxide is formed when two oxygen atoms chemically combine with a carbon atom. Which term best describes carbon dioxide?

• atom
• mixture
• element
• compound

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If a material contains three elements joined in a fixed proportion, it is a(n)

• Mixture
• Solution
• Atom
• Compound

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According to the chemical formula for sugar, how many Hydrogen (H) atoms are there?
C₁₂H₂₂O₁₁ 

• 11
• 12
• 10
• 22

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According to the chemical formula for salt, what is the ratio of sodium (Na) atoms to chlorine (Cl) atoms?
NaCl

• 2:2
• 0:0
• 1:1
• 2:1

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How would you write a chemical formula for a molecule that contains 6 carbon (C) atoms,16 hydrogen (H) atoms, and 5 oxygen (O) atoms?

• C₁₆H₅O₆
• C₆H₁₆O₅
• C₅H₁₆O₆
• C⁶H¹⁶O⁵

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How many oxygen (O) atoms are there in H₂O₂?

• 0
• 1
• 2
• 3

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NGSS.MS-PS1-1

A substance that is made up of only one kind of atom is a(n)

• compound
• element
• mixture
• solution