question_answer

Let \[{{N}_{\beta }}\] be the number of \[\beta \] particles emitted by 1 gram of \[N{{a}^{24}}\] radioactive nuclei (half-life = 15 hrs) in 7.5 hours, \[{{N}_{\beta }}\] is close to (Avogadro number\[=6.023\times {{10}^{23}}/g.\]mole): [JEE MAIN 11-04-2015]

A) \[6.2\times {{10}^{21}}\]

B) \[7.5\times {{10}^{21}}\]

C) \[1.25\times {{10}^{22}}\]

D) \[1.75\times {{10}^{22}}\]

Correct Answer: B

Solution :

[b] Half-life = 15 hrs.

moles of Na

No. of  particles (disintegrations)

moles

no. of particles