This question tests understanding of types of radioactive decay. The nucleus changes from K-40 (Z=19) to Ca-40 (Z=20), showing atomic number increases by 1 while mass number remains at 40. Beta-minus decay converts a neutron into a proton, emitting an electron and increasing Z by 1 without changing A since total nucleons are conserved. An alpha particle would decrease both Z and A, while a positron would decrease Z. Choice A incorrectly suggests gamma photons can increase mass number, reflecting the misconception that photons carry mass. When Z increases by 1 with constant A, the emitted particle must be an electron from beta-minus decay.

This question tests understanding of types of radioactive decay. The nucleus transforms from Po-210 (Z=84, A=210) to Pb-206 (Z=82, A=206), showing decreases of 2 in atomic number and 4 in mass number. Alpha decay emits a helium-4 nucleus containing 2 protons and 2 neutrons, producing exactly these changes: ΔZ = -2 and ΔA = -4. Beta decays would only change Z by 1 without affecting A, while gamma decay changes neither value. Choice B incorrectly suggests gamma decay can lower mass number, revealing the misconception that photons have mass. The simultaneous decrease of Z by 2 and A by 4 is the unique signature of alpha decay.

This question tests understanding of types of radioactive decay. The nucleus transitions from excited Tc-99 (indicated by asterisk) to ground-state Tc-99, with both mass number (A=99) and atomic number (Z=43) remaining unchanged. Gamma decay is the only process where a nucleus releases energy without changing its composition, emitting a photon as it transitions from a higher to lower energy state. The detected photon is the gamma ray carrying away the excess energy. Choice C incorrectly claims beta-minus decay decreases A, but beta decay never changes mass number, only atomic number. When an excited nucleus (marked with *) becomes the same nucleus without *, it's always gamma decay with no change in A or Z.

This question tests understanding of types of radioactive decay. Polonium-210 changes to lead-206, showing mass number decreases from 210 to 206 (by 4) and atomic number decreases from 84 to 82 (by 2). These changes match alpha decay perfectly, where a helium nucleus (2 protons, 2 neutrons) is emitted. Beta decays would only change Z by 1 while keeping A constant, and gamma decay changes neither value. Choice B incorrectly suggests gamma rays reduce mass number, confusing energy emission with particle emission. When both A and Z decrease by 4 and 2 respectively, alpha decay is the only possibility.

This question tests understanding of types of radioactive decay. Gamma decay involves an excited nucleus releasing excess energy as a high-energy photon (gamma ray) without changing its nuclear composition. Since no nucleons are added or removed, both mass number A and atomic number Z remain unchanged. The nucleus simply transitions from a higher to lower energy state. Choice D incorrectly suggests mass increases with energy gain, confusing mass-energy equivalence with actual nucleon count. Choice B would indicate beta decay, not gamma. Remember that gamma rays are pure electromagnetic energy with no mass or charge, so they cannot change A or Z.

This question tests understanding of types of radioactive decay. An alpha particle consists of 2 protons and 2 neutrons (helium-4 nucleus), so when emitted, it removes exactly these nucleons from the parent nucleus. The mass number A decreases by 4 (total nucleons lost) and atomic number Z decreases by 2 (protons lost). This is the defining characteristic of alpha decay. Choice B reverses the changes, showing confusion about alpha particle composition. Choice C suggests only Z changes, which would be beta decay, not alpha. Remember that alpha particles are helium nuclei with specific composition: 2 protons and 2 neutrons.

This question tests understanding of types of radioactive decay. A positron is the antiparticle of an electron with positive charge, emitted during beta-plus decay. In this process, a proton converts to a neutron plus a positron (and neutrino), decreasing the atomic number Z by 1. The mass number A remains constant since the total nucleon count doesn't change. Choice A describes beta-minus decay where Z increases, showing confusion between the two beta decay types. Choice C describes alpha decay, not positron emission. To distinguish beta decays, remember: positron emission means a proton becomes a neutron, so Z decreases.

This question tests understanding of types of radioactive decay. In beta-minus decay, a neutron within the nucleus converts into a proton, an electron, and an antineutrino. The electron (beta particle) and antineutrino are emitted, while the proton remains in the nucleus. This conversion increases the atomic number Z by 1 since there's now one more proton. The mass number A stays constant because the total number of nucleons (protons plus neutrons) remains unchanged. Choice A describes beta-plus decay where Z decreases, showing confusion between the two beta decay types. To remember beta-minus effects, think: neutron becomes proton, so Z increases by 1.

This question tests understanding of types of radioactive decay. The excited cobalt-60 nucleus (marked with *) becomes ground-state cobalt-60 with no change in mass number (60) or atomic number (27). Gamma decay occurs when an excited nucleus releases energy as a photon without changing its composition. Alpha decay would decrease A by 4 and Z by 2, while beta decays would change Z by 1. Choice C incorrectly claims beta-minus decay increases mass number, revealing a misconception that particle emission always changes A. When a nucleus transitions from excited to ground state with unchanged A and Z, gamma decay is occurring.

This question tests understanding of types of radioactive decay. The uranium-238 nucleus changes to thorium-234, showing the mass number decreases from 238 to 234 (by 4) and the atomic number decreases from 92 to 90 (by 2). In alpha decay, a helium nucleus (2 protons and 2 neutrons) is emitted, which accounts for exactly these changes: A decreases by 4 and Z decreases by 2. Beta decay would change Z by 1 while keeping A constant, and gamma decay changes neither A nor Z. Choice B (gamma decay) represents a common misconception that any radioactive decay involves photon emission. To identify decay type, always check how both mass number and atomic number change.