Alpha Decay and Nuclear Changes

Steps:

• An alpha particle is a helium-4 nucleus with 2 protons and 2 neutrons.
• Proton number (Z) equals the number of protons in the nucleus.
• Emitting an alpha particle removes 2 protons, so Z decreases by 2.
• Nucleon number (A) is the total protons plus neutrons; alpha emission removes 4 nucleons, so A decreases by 4.

Why A is correct:

• Alpha decay follows the rule: daughter nucleus has Z' = Z - 2 and A' = A - 4, as the alpha particle carries away 2 protons and 4 nucleons total.

Why the others are wrong:

• B: Nucleon decrease is 4, not 2, since alpha includes 2 neutrons.
• C: Emission removes particles, so numbers decrease, not increase.
• D: Proton change is -2, not +4; nucleon change is -4, not +2.

Final answer: A