Rachel has an unknown sample of a radioisotope listed in the table. using a special technique, she is able to measure the mass of just the unknown isotope as 104.8 kg at 12: 02: 00 p. m. at 4: 11: 00 p. m. on the same day, the mass of the unknown radioisotope is 13.1 kg. which radioisotope is in the sample?

Barium-139

Explanation:

initial mass of the sample at 12:02:00 PM is given as

Mass of the sample at 4:11:00 PM is given as

so here since it is a sample of radioactive isotope so here we will say

now from above data we know that the time taken to reduce the mass is

now from above equation we will have

so here half life is given as

So here this isotope must be the one which will have half life of 1.4 hours

So it is nearly Barium-139