Question

For beta-minus decay, which statement is TRUE?

• A. The daughter nuclide atomic mass \((A_D)\) is more than that of the parent nuclide atomic mass \((A_P)\)
• B. The daughter nuclide atomic number \((Z_D)\) is the same as that of the parent nuclide atomic number \((Z_P)\)
• C. The daughter nuclide neutron number \((N_D)\) is less than that of the parent nuclide neutron number \((N_P)\)
• D. The daughter nuclide neutron number \((N_D)\) is the same as that of the parent nuclide neutron number \((N_P)\)

Hint:

In beta-minus decay a neutron becomes a proton: A stays, Z goes up by one, N drops by one.

Answer 1

The Correct Option is C

Step 1: In beta-minus decay a neutron inside the nucleus turns into a proton, emitting an electron and an antineutrino: \[n \;\to\; p + e^- + \bar{\nu}_e.\] The nuclear reaction is \[{}^{A}_{Z}X \;\to\; {}^{A}_{Z+1}Y + e^- + \bar{\nu}_e.\]

Step 2: Track each number. The mass number stays the same, \(A_D = A_P\), because a neutron simply becomes a proton and the total nucleon count is unchanged.

Step 3: The atomic number rises by one, \(Z_D = Z_P + 1\), since a new proton is created.

Step 4: The neutron number drops by one, because one neutron was consumed: \[N_D = N_P - 1.\] So \(N_D\) is less than \(N_P\).

Step 5: Check the options against these facts. (A) \(A_D > A_P\) is false since \(A\) is unchanged. (B) \(Z_D = Z_P\) is false since \(Z\) increases. (D) \(N_D = N_P\) is false since \(N\) decreases. Only (C), \(N_D < N_P\), is correct.

\[\boxed{N_D = N_P - 1 < N_P}\]