A radio isotope 'X' with a half life 1.4 × 10⁹ years decays

Last updated: 7/31/2022

A radio isotope 'X' with a half life 1.4 × 10⁹ years decays to 'Y' which is stable. A sample of the rock from a cave was found to contain 'X' and 'Y' in the ratio 1: 7. The age of the rock is 1.96 × 10 years 3.92 × 10 years 4.20 × 10 years 8.40 × 10 years