Alpha decay effect: the emission of an alpha (α) particle from a nucleus changes the daughter nucleus in what way?

Introduction / Context:
Alpha decay is a common mode of radioactive decay among heavy nuclei. An alpha particle is a helium-4 nucleus consisting of 2 protons and 2 neutrons, so its emission alters both atomic number (Z) and mass number (A) of the parent nucleus.

Given Data / Assumptions:

• α particle = ^4He nucleus = 2p + 2n.
• Mass number A decreases by 4; atomic number Z decreases by 2 with each α emission.

Concept / Approach:
Conservation of nucleon number and charge dictates the daughter’s numbers: A_daughter = A_parent − 4; Z_daughter = Z_parent − 2. Hence both the atomic mass (proportional to A) and atomic number decrease.

Step-by-Step Solution:

Verification / Alternative check:
Example: ^238U → ^234Th + α. A: 238 → 234 (−4), Z: 92 → 90 (−2), consistent with the rule.

Why Other Options Are Wrong:

• More weight with less Z or less weight with more Z contradict conservation with α emission.
• Unchanged values or ”none of these” do not represent α decay.

Common Pitfalls:
Confusing α with β decay (β changes Z by ±1 with nearly unchanged A); overlooking that α removes two protons and two neutrons.

Final Answer:
Less atomic weight and less atomic number