Question 21

Question 21: A student looks up an element on the periodic table. The table says that the atomic number of the element is 12 and the mass number of the element is 40. What information do these two numbers convey about the element?

• The atomic number (12) represents the number of protons in the nucleus of the atom. The mass number (40) is the total number of protons and neutrons in the atom.

To find the number of neutrons, you subtract the atomic number from the mass number:

Number of neutrons = Mass number - Atomic number = 40 - 12 = 28.

Thus, the element has 12 protons and 28 neutrons.

Correct Answer: c. The element has 12 protons and has 28 neutrons.

Question 22: In all elements in a group, the thing that is the same is the:

• Elements in the same group (or column) of the periodic table have the same number of electrons in their valence shell, which determines their chemical properties and reactivity.

Correct Answer: a. Number of electrons in the valence shell.

Question 23: How many oxygen atoms are in the compound below:

Unfortunately, since the compound is not provided in your question, I cannot determine the answer. If you provide the specific compound (e.g., H₂O, CO₂, C₆H₁₂O₆, etc.), I can help identify the number of oxygen atoms present.

Please provide the compound for an accurate answer!