For the radioactive material half life is 10 minutes. If initially there are 800 number of nuclei the time taken (in minutes) for the disintegration of 600 nuclei is

20 minutes

The correct answer is option (3) : 20 minutes

600 Nuclei have been disintegrated, hence number of nuclei left = 200

Now, $\left(\frac{N}{N_0}\right)=\left(\frac{1}{2}\right)^n⇒\left(\frac{200}{800}\right)^n=\left(\frac{1}{2}\right)^n⇒n=2$

Time take for disintegration $=2\times 10=20 minutes$