Question

The half-life of a ratio-isotope is 4 h. If initial mass of the isotope was 200 g, then mass remaining after 24 h will be

• A. 1.042 g
• B. 2.084 g
• C. 3.125 g
• D. 4.167 g

Answer 1

Answer: (C)

3.125 g

Answer 2

$M = M_0 \big(\frac{1}{2}\big)^{t/t_{1/2}}$
$\therefore \, \, \, \, \, \, M =200 \big(\frac{1}{2}\big)^{24/4} = 200 \big(\frac{1}{2}\big)^6 = \frac{200}{64} = 3.125 \, g$