The half life of radium is about 1600 year. Of 100 gram of radium existing now

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The half life of radium is about 1600 year. Of 100 gram of radium existing now, 25g will remain unchanged after

Options

(a) 4800 year
(b) 6400 year
(c) 2400 year
(d) 3200 year

Correct Answer:

3200 year

Explanation:

100 gram at beginning, I = 0

25 gram remains undecayed.

N / N₀ = (1 / 2)ⁿ ⇒ 25 / 100 = (1 / 2)ⁿ

⇒ 1 / 4 = (1 / 2)ⁿ

Therefore, n = 2

Time = n × T

= 2 × 1600

= 3200 years.

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