The half life of radium is about 1600 years. Of 100 g of radium existing now, 25 g will remain unchanged after
- 4800 years
- 6400 years
- 2400 years
- 3200 years
Answer
(4) 3200 years
Solution
NN0 = ( 12 )n
⇒ 25100 = 14 = ( 12 )2
⇒ n = 2 half-lives
∴ t = n t1/2 = 2 1600 = 3200 years
Answer: (4)