NEET AIPMT SOLVED PAPER SCREENING 2004

  • question_answer
    The half-life of radium is about 1600 years. Of 100 g of radium existing now, 25 g will remain unchanged after:                                                                                                                                                                            

    A) 4800 year 

    B) 6400 year                    

    C) 2400 year     

    D) 3200 year

    Correct Answer: D

    Solution :

    Amount of substance remained is \[M={{M}_{0}}{{\left( \frac{1}{2} \right)}^{n}}\] Given, \[{{M}_{0}}=100g,\,\,M=25\,kgm,\,{{T}_{1/2}}\,=1600\] years So,                  \[25=100{{\left( \frac{1}{2} \right)}^{n}}\] or    \[\frac{25}{100}={{\left( \frac{1}{2} \right)}^{n}}\] or    \[{{\left( \frac{1}{2} \right)}^{2}}={{\left( \frac{1}{2} \right)}^{n}}\] Comparing the power, we have \[n=2\] or    \[\frac{t}{{{T}_{1/2}}}=2\] or\[t=2{{T}_{1/2}}=2\times 1600=3200\]years


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