Question

20 mg of C-14 has half-life of 5760 yr. 100 mg of sample containing C-14 is reduced to 25 mg in
A. 57600 yr
B. 1440 yr
C. 17280 yr
D. 11520 yr

Answer 1

Correct Answer - d
Half-life period for a nucleus is a constant quantity. It does not change with amount or mass. Hence, ltbRgt `t_(1//2) = 5760 yr, N = N_(0)((1)/(2))^((t)/(t_(1//2)))`
`(25)/(100) = ((1)/(2))^((t)/(5760)) or ((1)/(2))^(2) = ((1)/(2))^((t)/(5760))`
`:. (t)/(5760) = 2 or t = 2xx5760 = 11520 yr`