Elements, Compounds, Mixtures

Choose the substances that exist as atoms of elements.

• Xe

• Au

• Na

• O₂

• N₂

Choose the substances that exist as molecules of elements.

• Cl₂

• O₃

• H₂

• CO

• H₂O

Choose the substances that exist as molecules of compounds.

• O₂

• CH₄

• F₂

• CO

• NH₃

Choose the substances that exist as ions of compounds.

• H₂O

• MgCl₂

• CO₂

• FeCl₃

• K₂S

Select the false statement.

• An element is a pure substance that cannot be broken down into two or more simpler substances by chemical methods. 

• A compound is a pure substance containing two or more elements that are physically combined in a fixed ratio.

• A mixture is made up of two or more elements and/or compounds that are not chemically combined.

Which of the following are mixtures?

• Pure water

• Seawater

• Table salt

• Air

Which of the following are true about a mixture?

​ (a)   ​ (b)   ​ ​​ (c)  

• Has a variable composition

• Melts and boils over a range of temperatures

• Can separate into its components by physical means

• Has a fixed composition

• Has fixed melting and boiling points

Which diagram best represents molecules of elements? (a)  

• D
• A
• B
• C
• E

Which diagram best represents compounds?

• A

• B

• C

• D

• E

Which diagram best represents mixture? (a)  

• E
• A
• B
• C
• D