1.

2 g of a radioactive sample having half life of 15 days was synthesised on 1^(st) Jan 2009. The amount of the sample left behind on 1^(st) March, 2009 (including both the days)

Answer»

0.125 g
1 g
0.5 g
0g

Solution :No. of days from `1^(st)` Jan 09 to `1^(st)` March '09 = 60
GIVEN, `t_(1//2) = 15` days
Total time, `T = 60` days
`:.` No. of half-lives, n = ?
Also given, initial AMOUNT of sample, `N_(0) = 2g`
`:.` Sample PRESENT after 4 half lives, `N= ?`
`N = ((1)/(2))^(n) N_(0)`
`rArr N = ((1)/(2))^(4) xx 2 = (2)/(16) = 0.125g`


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