Question

. An isotope has a half-life of 7.0 h. How long
does it take for 90 percent of the sample to
remain?
a. 8.4x10^s
b. 2.7x10^s
c. 3.8x10's
d. 3.3x10^s
​

Answer 1

Answer: (c)

Explanation:

We know that  radioactive decay follows first order kinetics.                                                         so we can obtain a relation between number of radioactive nuclei taken initially and no of nuclei at that instant

N=N#×e*(-lt)                                                                                                                                here we are given that N/N# is 0.9 (ie 90%)                                                                    and l is decay constant  , decay constant =ln2/half life                                                                so by substituting all values in above equation we get time t =3.79×10³s