This question tests understanding of types of radioactive decay. In alpha decay, a nucleus emits an alpha particle (helium-4 nucleus), which has 2 protons and 2 neutrons, causing the mass number to decrease by 4 and atomic number to decrease by 2. Here, Po-210 (Z=84, A=210) becomes Pb-206 (Z=82, A=206), showing exactly these changes: mass number drops by 4 (210→206) and atomic number drops by 2 (84→82). Beta decay would only change atomic number by 1, while gamma decay changes neither mass nor atomic number. Choice A incorrectly claims gamma decay changes mass number, revealing confusion about gamma rays being massless photons. When analyzing nuclear decay, always check both mass and atomic number changes to identify the decay type.

This question tests understanding of types of radioactive decay. In gamma decay, an excited nucleus (indicated by 'm' for metastable) releases excess energy as a photon without changing its nuclear composition, leaving both mass number (A) and atomic number (Z) unchanged. Technetium-99m (Z=43, A=99) emits a gamma ray to become ground-state technetium-99 (Z=43, A=99), with no change in either A or Z. Alpha decay would decrease both values, while beta decays would change Z. The other choices all incorrectly claim changes in A or Z, missing that gamma emission is purely an energy transition. When a metastable isotope loses its 'm' designation without changing element or mass, gamma decay has occurred.

This question tests understanding of types of radioactive decay. In beta-plus decay (positron emission), a proton converts to a neutron by emitting a positron, decreasing the atomic number by 1 while mass number remains constant. Sodium-22 (Z=11, A=22) becomes neon-22 (Z=10, A=22), showing atomic number decreases by 1 (11→10) with unchanged mass number (22→22). Beta-minus decay would increase atomic number, while alpha decay would change both mass and atomic numbers. Choice B incorrectly claims beta-minus decay decreases atomic number, revealing confusion about the direction of charge change in beta decays. Remember that beta-plus decreases Z (proton lost) while beta-minus increases Z (proton gained).

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. 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. 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. 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.

This question tests understanding of types of radioactive decay. The nucleus transforms from F-18 (Z=9) to O-18 (Z=8) with mass number constant at 18, indicating atomic number decreases by 1 while mass number is unchanged. Beta-plus decay converts a proton into a neutron plus a positron, decreasing Z by 1 without changing A since the total nucleon count remains constant. Beta-minus would increase Z, while alpha decay would change both values. Choice C incorrectly attributes Z decrease to gamma decay, revealing the misconception that photons can change nuclear composition. When atomic number decreases by 1 with unchanged mass number, beta-plus decay is the only possible process.

This question tests understanding of types of radioactive decay. In beta-minus decay, a neutron converts to a proton by emitting an electron (beta particle), increasing the atomic number by 1 while mass number stays constant. Carbon-14 (Z=6, A=14) becomes nitrogen-14 (Z=7, A=14), showing atomic number increases by 1 (6→7) with unchanged mass number (14→14). Alpha decay would decrease both mass and atomic numbers, while gamma decay changes neither. Choice D incorrectly states beta-plus decay increases mass number, revealing the misconception that emitted particles add to nuclear mass rather than being created from existing nucleons. To identify decay type, compare initial and final atomic numbers and mass numbers systematically.