QCM : Fundamentals of Chemistry — 10 questions

Questions et réponses du QCM

1. What is a chemical element?

A substance formed when two or more elements are chemically bonded
A group of atoms bonded together representing the smallest unit of a compound
A pure substance made of only one type of atom
A charged particle with a net electric charge

A pure substance made of only one type of atom

Explication

An element is a pure substance consisting of only one type of atom, which is fundamental in chemistry. The other options describe compounds, molecules, or ions, which are different concepts.

2. What defines an atom in chemistry?

The smallest unit of an element that retains its chemical properties.
The smallest particle that makes up molecules.
A group of atoms bonded together with a net electric charge.
A pure substance formed by chemical bonding of two or more elements.

The smallest unit of an element that retains its chemical properties.

Explication

An atom is the smallest unit of an element that retains its chemical properties, making it fundamental to understanding elements in chemistry.

3. What is the atomic number of Iron (Fe)?

26
30
24
28

26

Explication

The atomic number of Iron (Fe) is 26, which is a well-known fact listed in the periodic table and supported by the content's emphasis on elements and their symbols.

4. Which of the following correctly describes a molecule?

Two or more atoms chemically bonded together, representing the smallest unit of a compound.
A single atom that has lost or gained electrons.
A pure substance consisting of only one type of atom.
A mixture of different elements physically combined.

Two or more atoms chemically bonded together, representing the smallest unit of a compound.

Explication

A molecule consists of two or more atoms bonded together, whether they are the same element or different, and is the smallest unit of a compound.

5. What is the primary role of atoms and molecules in matter?

They serve as catalysts to speed up chemical reactions.
They are primarily involved in the physical state changes of matter.
They are the basic units that make up elements and compounds, determining the properties of substances.
They are responsible for energy transfer and storage within cells.

They are the basic units that make up elements and compounds, determining the properties of substances.

Explication

Atoms are the fundamental units of elements, and molecules are formed when atoms bond chemically, representing the smallest units of compounds. Their primary role is to constitute matter and determine its properties, making option 0 correct. The other options describe secondary or specific functions, but not their main role.

6. Which statement accurately reflects an element?

It is a pure substance made of only one type of atom, characterized by its atomic number.
It is any substance that has a variable composition.
It always consists of molecules with multiple atoms.
It is a mixture of different compounds.

It is a pure substance made of only one type of atom, characterized by its atomic number.

Explication

An element is a pure substance made of only one type of atom, distinguished by its atomic number, which defines its chemical properties.

7. What is the primary difference between physical and chemical properties?

Physical properties can be observed without changing the substance; chemical properties involve reactivity and change.
Physical properties involve reactivity; chemical properties are only measurable without change.
Physical properties are fixed; chemical properties vary depending on conditions.
Physical properties describe a substance's chemical composition; chemical properties describe its color.

Physical properties can be observed without changing the substance; chemical properties involve reactivity and change.

Explication

Physical properties, such as melting point, can be observed without changing the substance, whereas chemical properties involve how a substance reacts and transforms.

8. Which of the following is an example of an extensive property?

Mass of a substance
Density of a substance
Color of a substance
Boiling point of a substance

Mass of a substance

Explication

Mass is an extensive property because it depends on the amount of matter present, unlike density or boiling point, which are intensive properties.

9. What does the oxidation number of an atom indicate?

The charge of an atom in a compound or ion.
The number of protons in the nucleus.
The total number of electrons in the atom.
The atomic mass of an element.

The charge of an atom in a compound or ion.

Explication

The oxidation number reflects the charge an atom appears to have within a compound, based on electron sharing or transfer.

10. Who authored the periodic table in 1869, which organized elements by atomic number?

Dmitri Mendeleev
John Dalton
Henri Becquerel
Dmitri Ivanovich Mendeleev

Dmitri Mendeleev

Explication

Dmitri Mendeleev is credited with creating the periodic table in 1869, organizing elements by increasing atomic weight and properties, which later evolved to atomic number.

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Matter — definition?

Anything that has mass and occupies space

Matter — definition?

Anything with mass and occupying space.

Atom — role?

Smallest unit of an element retaining its properties

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