Question

isotopes of an element always have the same
a mass number
b number of neutrons
c number of subatomic particles
d atomic number

question 39
1 point
let z represent atomic number, a represent mass number, and n represent the number of neutrons in an atom. which of the following is correct?
a n = a + z
b z = a + n
c n = a - z
d a = n - z

Explanation:

Question 38 (Isotopes question)

Isotopes are atoms of the same element with the same atomic number (number of protons) but different mass numbers (due to different numbers of neutrons).

• Option A: Mass number differs for isotopes (since neutrons differ), so A is wrong.
• Option B: Number of neutrons differs in isotopes, so B is wrong.
• Option C: Subatomic particles (protons + neutrons + electrons) differ because neutrons differ, so C is wrong.
• Option D: Atomic number (protons) is same for isotopes of an element, so D is correct.

Mass number (\(A\)) is the sum of protons (atomic number, \(Z\)) and neutrons (\(N\)). So \(A = Z + N\). Rearranging gives \(N = A - Z\).

• Option A: \(N = A + Z\) is incorrect (adds instead of subtracts).
• Option B: \(Z = A + N\) is incorrect (mass number is sum, not atomic number).
• Option C: \(N = A - Z\) matches the rearrangement, so correct.
• Option D: \(A = N - Z\) is incorrect (wrong rearrangement).

Answer:

D. Atomic number

Question 39 (Atomic structure formula)