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WB JEE Medical WB JEE Medical Solved Paper-2006

  • question_answer
    By dissolving 5 g substance in 50 g of water, the decraease in freezing point is \[1.2{{\,}^{o}}C.\] The gram molal depression is \[1.85{{\,}^{o}}C.\] The molecular weight of substance is :

    A)  105.4                                   

    B)  118.2

    C)  137.2                                   

    D)  154.2

    Correct Answer: D

    Solution :

                     We know that \[m=\frac{1000{{K}_{f}}\times w}{\Delta TW}\] Here, \[\Delta T=1.2{{\,}^{o}}C,{{K}_{f}}={{1.85}^{o}}\]                 \[w=5g,W=50g\]                 \[\therefore \]  \[m=\frac{1000\times 1.85}{1.2\times 50}=154.2\]


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