Medium MCQ +4 / -1 PYQ · JEE Mains 2021

The half-life of ${}^{198}Au$ is 3 days. If atomic weight of ${}^{198}Au$ is 198 g/mol then the activity of 2 mg of ${}^{198}Au$ is [in disintegration/second] :

  1. A 2.67 $\times$ 10<sup>12</sup>
  2. B 6.06 $\times$ 10<sup>18</sup>
  3. C 32.36 $\times$ 10<sup>12</sup>
  4. D 16.18 $\times$ 10<sup>12</sup> Correct answer

Solution

A = $\lambda$N<br><br>$$\lambda = {{\ln 2} \over {{t_{1/2}}}} = {{\ln 2} \over {3 \times 24 \times 60 \times 60}}$$sec<sup>$-$1</sup> = 2.67 $\times$ 10<sup>$-$6</sup> sec<sup>$-$1</sup><br><br>N = Number of atoms in 2 mg Au<br><br>$= {{2 \times {{10}^{ - 3}}} \over {198}} \times 6 \times {10^{23}}$ = 6.06 $\times$ 10<sup>15</sup><br><br>$A = \lambda N = 1.618 \times {10^{13}} = 16.18 \times {10^{12}}$ dps

About this question

Subject: Physics · Chapter: Atoms and Nuclei · Topic: Bohr's Model of Hydrogen Atom

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