Question

75 atoms of a radioactive species are decayed in 2 half-lives $(t_{1/2}=1hr)$ if 100 atoms are taken initially. Number of atoms decayed if 200 atoms are taken in 2 hr are:

• A. 75
• B. 150
• C. 50
• D. 200

Answer 1

The correct option is B 150

$N=\frac{N_0}{2^n}=\frac{N_0}{2^2}=\frac{N_0}{4}(t_{1/2}=2\therefore T=n\times t_{1/2})$
or $\frac{200}{4}=50atomsareleftand150aredecayed$