Effect of beta (β) decay on nuclear composition: compared to the parent, the new nucleus formed after β-decay has which change?

Introduction / Context:
Beta (β−) decay is a common nuclear transformation in which a neutron converts to a proton with the emission of an electron and an antineutrino. Understanding how β-decay affects atomic number and mass number is foundational in nuclear chemistry and decay-chain calculations.

Given Data / Assumptions:

• We refer to β− decay (not β+ or electron capture).
• Products: daughter nucleus, electron (beta particle), and antineutrino.
• Neglect the tiny mass of the emitted electron relative to nucleon masses when discussing mass number.

Concept / Approach:
In β− decay, a neutron in the nucleus changes into a proton: n → p + e− + anti-ν. The number of protons (atomic number Z) increases by one, while the total number of nucleons (mass number A) remains the same because one neutron is replaced by one proton. Hence, atomic number increases, mass number is unchanged.

Step-by-Step Solution:
Start with parent nucleus (Z, A).After β− decay: (Z + 1, A) because neutron → proton.Compare to options: “More atomic number” matches exactly.

Verification / Alternative check:
Decay series diagrams consistently show β− steps moving one place to the right on the periodic table (higher Z) while staying in the same horizontal mass-number row (same A).

Why Other Options Are Wrong:

• Less atomic number: Opposite direction; would match β+ or electron capture.
• Less or more atomic weight: Atomic/molar mass changes minimally; mass number unchanged.
• Lower mass number by one: Incorrect; A is constant in β− decay.

Common Pitfalls:
Confusing β− with β+; assuming mass number changes because a particle is emitted—mass number counts nucleons only.

Final Answer:
More atomic number