1.

0.1 g atom of radioactive isotope ""_ZX^A (half-life 5 days) is taken. How many number of atoms will decay during eleventh day?

Answer»

SOLUTION :`N_0 = 0.1 atom`
`t = 10" daysand" t_(1//2) = 5` days
`LAMBDA = 2.303/t log""N_0/N`
`0.693/5 = 2.303/10 log""0.1/N`
`:.`Amount left after 10 days = 0.0250 g atom
Similarly if t = 11 days
`0.693/5 = 2.303/11 log""0.1/N`
`:.` Amount left after 11 days = 0.0218 g atom
`:.` Amount decayed in 11th DAY =0.0250- 0.0218
`= 3.2xx 10^(-3)` g atom
`=3.2 XX 6.023 xx 10^23 xx 10^(-3)" atoms" = 1.93 xx 10^21` atoms


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