Chemistry Quiz

What is the atomic number of an element?

• The number of protons in the nucleus

• The number of electrons in the nucleus

• The sum of protons and neutrons in the nucleus

• The number of neutrons in the nucleus

Answer explanation

The atomic number of an element is defined as the number of protons in its nucleus. This number determines the element's identity and its position in the periodic table.

The mass number of an element is equal to.

• The number of protons

• The number of neutrons

• The number of electrons

• The number of protons and neutrons

Answer explanation

The mass number of an element is the total count of protons and neutrons in its nucleus. Therefore, the correct answer is 'The number of protons and neutrons'.

Isotopes of an element have the same number of:

• Electrons

• Protons

• Neutrons

• Both (a) and (c)

Answer explanation

Isotopes of an element have the same number of protons, which defines the element, but differ in the number of neutrons. Therefore, the correct answer is 'Protons'.

The symbol H2O represents:

• One molecule of hydrogen and two molecules of oxygen

• Two molecules of hydrogen and one molecule of oxygen

• One atom of hydrogen and two atoms of oxygen

• Two atoms of hydrogen and one atom of oxygen

Answer explanation

The symbol H2O indicates that there are two atoms of hydrogen (H) and one atom of oxygen (O) in a water molecule, making 'Two atoms of hydrogen and one atom of oxygen' the correct choice.

The molecular formula of ammonia is:

• NH3

• NH4

• NH2

• ANH3

Answer explanation

The molecular formula of ammonia is NH3, which consists of one nitrogen (N) atom and three hydrogen (H) atoms. The other options, NH4 and NH2, represent different species, while ANH3 is not a valid formula.

How many moles of carbon atoms are present in one mole of methane (CH4)?

• 1 mole

• 2 moles

• 4 moles

• 6 moles

Answer explanation

In one mole of methane (CH4), there is one carbon atom. Therefore, the number of moles of carbon atoms present is 1 mole, making the correct answer 1 mole.

The molar mass of water (H2O) is approximately:

• 18 g/mol

• 22 g/mol

• 16 g/mol

• 24 g/mol

Answer explanation

The molar mass of water (H2O) is calculated by adding the molar masses of its components: 2 hydrogen atoms (1 g/mol each) and 1 oxygen atom (16 g/mol), resulting in 2 + 16 = 18 g/mol, making 18 g/mol the correct answer.

Which of the following represents a cation?

• Cl

• H+

• O2

• N3-

Answer explanation

A cation is a positively charged ion. Among the options, H+ represents a hydrogen ion with a positive charge, making it a cation. Cl is neutral, O2 is a neutral molecule, and N3- is an anion with a negative charge.

The chemical formula of sodium carbonate is:

• Na2CO3

• NaHCO3

• Na2CO2

• NaCO3

Answer explanation

The correct chemical formula for sodium carbonate is Na2CO3, which consists of two sodium (Na) ions, one carbonate (CO3) ion. The other options represent different compounds: NaHCO3 is sodium bicarbonate, Na2CO2 is not a standard formula, and NaCO3 is incorrect.

The formula of carbon dioxide is:

• CO

• CO2

• CO3

• C2O

Answer explanation

The correct formula for carbon dioxide is CO2, which consists of one carbon atom and two oxygen atoms. The other options do not accurately represent the composition of carbon dioxide.