Compounds & Molecules (Difficult)

Hydrogen is a pure substance represented by the chemical symbol H. Which of the following best describes hydrogen?

• Hydrogen is an element made of two or more kinds of atoms.
• Hydrogen is a compound made of only one kind of atom.
• Hydrogen is a compound made of two or more kinds of atoms.
• Hydrogen is an element made of only one kind of atom.

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.

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

The chemical combination of two or more different kinds of atoms in fixed amounts is called a(n)

• orbit
• compound
• mixture
• element

Atoms combine to form _______. 

• electrons
• molecules
• nuclei
• neutrons

A compound is...

• a substance made up of one type of atom in its molecular form.
• a substance formed by the reaction of two or more elements.
• a mixture formed by the mixing of two or more elements.
• a substance made up of one type of atom in its atomic form.

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

• atom
• mixture
• element
• compound

What defines a mixture?

• described by a chemical formula
• can be broken down into its basic substances through physical means
• created through a chemical reaction
• cannot be broken down into simpler substances

The air we breathe contains different individual gases (mostly nitrogen and oxygen). Which of the following correctly describes the air we breathe?

• compound
• liquid
• element
• mixture