Question

Radium decays to form radon. Which equation correctly describes this decay?

Superscript 226 Subscript 88 Baseline Upper R a right arrow Superscript 222 Subscript 84 Baseline Upper R n + Superscript 4 Subscript 4 Baseline Upper H e

Superscript 226 Subscript 88 Baseline Upper R a right arrow Superscript 222 Subscript 86 Baseline Upper R n + Superscript 0 Subscript negative 1 Baseline e

Superscript 226 Subscript 88 Baseline Upper R a right arrow Superscript 222 Subscript 86 Baseline Upper R n + Superscript 0 Subscript + 1 Baseline e

Superscript 226 Subscript 88 Baseline Upper R a right arrow Superscript 222 Subscript 86 Baseline Upper R n + Superscript 4 Subscript 2 Baseline Upper H e

Answer 1

The correct equation is:

^226_88Ra → ^222_86Rn + ^4_2He

Reason: This is alpha decay (emission of a ^4_2He nucleus). Mass numbers: 226 = 222 + 4; atomic numbers: 88 = 86 + 2.