12th Class Chemistry Nuclear Chemistry Question Bank Critical Thinking Nuclear chemistry

  • question_answer The half-life of a radioactive isotope is three hours. If the initial mass of the isotope were 256 g, the mass of it remaining undecayed after 18 hours would be [AIEEE 2003]

    A)            4.0 g                                        

    B)            8.0 g

    C)            12.0 g                                      

    D)            16.0 g

    Correct Answer: A

    Solution :

           \[{{N}_{t}}={{N}_{o}}{{\left( \frac{1}{2} \right)}^{n}}\], \[{{N}_{t}}=256\ {{\left( \frac{1}{2} \right)}^{18/3}}\]\[=256\ {{\left( \frac{1}{2} \right)}^{6}}=4\].

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