The radioactive hydrogen isotope 3H is called tritium. It decays by beta-minus decay with a half-life of 12.3 years.
Part A: What is the daughter nucleus of tritium?
Part B:
A watch uses the decay of tritium to energize its glowing dial. What fraction (N/No in percentage) of the tritium remains 20 years after the watch was created? Express your answer using two significant figures.