Question

The activity of a radioactive element decreased to one-third of the original activity I₀ in a period of nine years. After a further lapse of nine years its activity will be-

• A. I₀
• B. (2/3) I₀
• C. I₀/9
• D. I₀/6

Answer 1

Answer: (C)

I₀/9

Answer 2

= ̃ $\frac { 1 } { 3 }$ =

= $\left( \frac { 1 } { 2 } \right) ^ { 18 / \mathrm { T } }$ = ̃ I' = $\frac { \mathrm { I } _ { 0 } } { 9 }$