An atom of 25Mg contains __ electrons. A) 25 B) 37 C) 13 D) 23 E) 12
The Correct Answer and Explanation is :
The correct answer is E) 12.
Explanation:
To understand how many electrons an atom of (^{25}Mg) (magnesium-25) contains, we need to break down the information given and apply basic atomic structure principles.
- Atomic Number: The atomic number of magnesium (Mg) is 12, which means every magnesium atom, regardless of its isotope, has 12 protons in its nucleus. In a neutral atom (i.e., one that is not ionized), the number of protons is equal to the number of electrons, because the atom must have a balance of positive and negative charges.
- Isotopes: The notation (^{25}Mg) refers to an isotope of magnesium, specifically magnesium-25. The number 25 is the mass number, which is the total number of protons and neutrons in the nucleus of the atom. The mass number does not affect the number of electrons directly. It tells us that this particular isotope of magnesium has 25 total nucleons (protons + neutrons), with 12 of those being protons (since magnesium always has 12 protons). Therefore, the number of neutrons in magnesium-25 is: [
\text{Neutrons} = \text{Mass number} – \text{Protons} = 25 – 12 = 13 \text{ neutrons}
] - Electrons in a Neutral Atom: In a neutral atom, the number of electrons equals the number of protons. Since magnesium has 12 protons, the neutral atom of (^{25}Mg) will also have 12 electrons.
Thus, magnesium-25 (whether it is the isotope in question or just magnesium in general) will have 12 electrons, making the correct answer E) 12.