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Atoms and molecules combine to form all the matter we see in our universe. They have unique identities that characterize them and separate them from one another. Atoms can bond together to make larger samples of matter, such as compounds. Atoms are also found in mixtures. Which statement correctly contrasts a compound and a mixture?

• A compound is made of a fixed ratio of two or more elements chemically combined, and a mixture can contain two or more compounds physically combined.

• A compound contains two or more elements that are physically combined, and a mixture contains two or more compounds that are chemically combined.

• A mixture combines to form a compound that cannot be separated physically, and a compound displays physical characteristics of the mixture.

• A compound and mixture differ in the number of elements they contain, and both cannot be separated physically or chemically.

Which of these statements correctly describes the trends when moving from left to right within the period from sodium to chlorine?

• The number of valence electrons increases, and the atomic radius increases.

• The number of valence electrons increases, and the atomic radius decreases.

• The number of valence electrons decreases, and the atomic radius increases.

• The number of valence electrons decreases, and the atomic radius decreases.

Which of the samples shown represents a pure substance?

• substances 1 and 2

• substances 2 and 3

• substances 3 and 4

• substances 1 and 4

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NGSS.MS-PS1-1

The periodic table of the elements organizes elements according to their properties. A section of the periodic table is shown.

Which set of elements below is the most similar in chemical behavior?

• H, Be, Sc

• Fr, Ra, Rf

• Ti, V, Cr

• Be, Ca, Ra

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NGSS.MS-PS1-1

Two common liquids, water and peroxide, are both formed with atoms of hydrogen and oxygen. If both substances discussed above are made of hydrogen and oxygen, how is the make-up of the two substances different?

• The number of atoms of each element is different.

• The number of protons in the atoms of each element is different.

• The number of protons in the atoms of each element is different.

• The number of protons in the atoms of each element is different.

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NGSS.MS-PS1-1

Since sodium chloride is classified as a compound, a sample of it contains...

• atoms that are gases, liquids, and solids.

• more than one kind of atom

• matter than cannot be reduced into atoms

• a solution of atoms and molecules

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NGSS.MS-PS1-1

What do carbon, hydrogen, and oxygen atoms have in common?

• the same number of protons

• he same number of electrons

• neutrons located outside of the nucleus

• electrons located outside of the nucleus

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NGSS.MS-PS1-1

Sodium metal (Na) reacts violently when mixed with water and produces sodium hydroxide (NaOH) and hydrogen gas (H2).

Which metal would most likely react in a similar fashion?

• magnesium (Mg)

• aluminum (Al)

• potassium (K)

• titanium (Ti)

The mass of an element is the sum of the atomic number and the number of __________.

• electrons

• ions

• neutrons

• protons

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NGSS.MS-PS1-1

Which of these is not an example of a pure substance?

• aluminum can

• milk

• table salt

• water