The number of protons and neutrons in an atom of magnesium-25 is: 1) 25 protons and 12 neutrons 2) 12 protons and 25 neutrons 3) 25 protons and 37 neutrons 4) 12 protons and 13 neutrons 5) 13 protons and 12 neutrons Question 2 (2 points) List the number of protons, neutrons, and electrons for 35CI: 1) 35 protons, 18 neutrons, and 18 electrons 2) 18 protons, 17 neutrons, and 17 electrons 3) 17 protons, 18 neutrons, and 18 electrons
The Correct Answer and Explanation is:
Based on the chemical principles for determining the composition of atoms and ions, here are the correct answers and explanations for the questions provided in the image.
Correct Answers:
- Question 1: 4) 12 protons and 13 neutrons.
- Question 2: 3) 17 protons, 18 neutrons, and 18 electrons.
Explanation
Question 1: The number of protons and neutrons in an atom of magnesium-25 is:
To solve this, we need two key pieces of information from the name “magnesium-25”.
First, the element is magnesium (Mg). The identity of an element is determined by its atomic number, which is equal to the number of protons in its nucleus. By looking at a periodic table, we find that magnesium’s atomic number is 12. Therefore, any atom of magnesium must contain 12 protons.
Second, the number “25” represents the mass number of this specific magnesium isotope. The mass number is the total count of protons and neutrons in the nucleus. We can calculate the number of neutrons using the formula:
Number of Neutrons = Mass Number – Number of Protons
Number of Neutrons = 25 – 12 = 13
Thus, an atom of magnesium-25 contains 12 protons and 13 neutrons. This corresponds to option 4.
Question 2: List the number of protons, neutrons, and electrons for ³⁵Cl:
This question requires us to analyze the isotope notation ³⁵Cl.
First, the element symbol “Cl” stands for chlorine. The atomic number of chlorine is 17. This means a chlorine atom or ion always has 17 protons. This fact alone eliminates options 1 and 2.
The superscript “35” is the mass number. We can find the number of neutrons by subtracting the number of protons from the mass number:
Number of Neutrons = 35 – 17 = 18 neutrons.
Finally, we determine the number of electrons. A neutral atom has an equal number of electrons and protons. A neutral chlorine atom would have 17 electrons. However, this choice is not available. Option 3 lists 18 electrons. An atom with 17 protons (positive charges) and 18 electrons (negative charges) has a net charge of -1. This describes the chloride ion (Cl⁻), which is the stable and common form of chlorine. The question likely refers to this stable ion. Therefore, ³⁵Cl⁻ has 18 electrons. This matches option 3.
