The half life of a radio active substance is 10 days. This means that

Moderate

A

The substance completely disintegrates in 20 days.
B

The substance completely disintegrates in 40 days.
C

1/8 part of the total number of active nuclei of the substance will be left infact at the end of 40 days.
D

7/8 th part of the total number of active nuclei of the substance disintegrates in 30 days.

Solution

After 30 days (i.e. 3 half lives) number of active nuclei left is given by $N = \frac{N_{0}}{{(2)}^{\frac{3 T}{3}}} = \frac{N_{0}}{8}$ .
So total number of nuclei disintegrates in 30 days $= N_{0} - \frac{N_{0}}{8} = \frac{7}{8} N_{0}$

Get Instant Solutions

When in doubt download our app. Now available Google Play Store- Doubts App

Recieve an sms with download link

SCAN ME