Question

The half-life of a radioisotope is 6.93 hours. If initial mass of the isotope is 200 g, the mass
(in g) of the remaining undecayed isotope after 46.06 hours is
20.0
(A)
(B) 4.2
(C) 2.0
(D) 0.2
1​

Answer 1

Half life of a radio isotope = 6.93 hours

Initial mass = 200 g

We need to find the remaining undecayed isotope after 46.06 hours

In order to find the no of half lives

46.06 / 6.93=7

We need to find the amt of substance left after 7 half lives

First : 200-->100

Second:100-->50

Third:50-->25

Fourth:25-->12.5

Fifth:12.5-->6.25

Sixth:6.25-->3.125

Seventh: 3.125-->1.56

the amount of undecayed isotope is 1.56 g which is approximately equal to 2

the ans is c