One gram of a radioactive substance of half life 4 days is sealed in a tube. The quantity left after 5 days is

Options

A. 460 mg
B. 240 mg
C. 420 mg
D. 402 mg

Answer

C

Explanation

`"log" N_(0)/N=(lambda t)/2.303=(0.693 t)/(2.303 T)`
`:. "log"N_(0)/N=(0.693xx5)/(2.303xx4)=3.465/9.212 =0.3761`
anti `log ("log" N_(0)/N)=0.3761`
`:. N_(0)/N=2.378`
`N=N_(0)/2.378`
`=1/2.378 =0.420` gm