Question

1. an atom is the smallest unit of an element that retains the chemical properties of that element.

a) true b) false

1. which of the following is an example of an element?

a) water (h₂o) b) carbon dioxide (co₂) c) oxygen (o₂) d) sugar (c₁₂h₂₂o₁₁)

1. a molecule is always made up of atoms of different elements chemically bonded together.

a) true b) false

1. which of the following is an example of a molecule?

a) iron (fe) b) helium (he) c) salt (nacl) d) neon (ne)

1. in the gas state, particles are closely packed together and vibrate in fixed positions.

a) true b) false

Explanation:

1. By definition, an atom is the smallest unit of an element that retains its chemical properties.
2. An element is a pure substance made of only one type of atom. Oxygen ($O_2$) is an element, while the others are compounds.
3. A molecule can be made up of atoms of the same element (e.g., $O_2$) or different elements. So the statement is false.
4. A molecule is a group of two or more atoms held together by chemical bonds. Salt (NaCl) is a molecule as it consists of sodium and chlorine atoms bonded together. Iron, helium and neon are elements, not molecules in the context of this question.
5. In the gas - state, particles are far apart and move freely, not closely packed and vibrating in fixed positions.

Answer:

1. a) True
2. c) Oxygen ($O_2$)
3. b) False
4. c) Salt (NaCl)
5. b) False