Question

Gold can undergo transmutation. Which equation could correctly describe this radioactive decay?

Superscript 185 Subscript 79 Baseline Upper A u right arrow Superscript 181 Subscript 77 Baseline Upper Re + Superscript 4 Subscript 2 Baseline Upper H e

Superscript 185 Subscript 79 Baseline Upper A u right arrow Superscript 181 Subscript 77 Baseline Upper I r + Superscript 4 Subscript 2 Baseline Upper H e

Superscript 185 Subscript 79 Baseline Upper A u right arrow Superscript 181 Subscript 77 Baseline Upper I r + Superscript 0 Subscript negative 1 Baseline e

Superscript 185 Subscript 79 Baseline Upper A u right arrow Superscript 181 Subscript 77 Baseline Upper I r + Superscript 0 Subscript positive 1 Baseline e

Answer 1

The second equation:

^185_79Au → ^181_77Ir + ^4_2He

Reason: an alpha particle (4,2 He) carries away 4 mass units and 2 protons, so 185 → 181 and 79 → 77. The other options either don't conserve mass number or give the wrong change in atomic number.