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JEE Main & Advanced Sample Paper JEE Main - Mock Test - 5

  • question_answer
    \[100mL\] samples of distilled water and boiled water required, respectively, \[2mL,\] \[17mL,\] and\[7mL\] of soap solution to form permanent lather. The ratio of permanent to temporary hardness in the tap water is

    A) \[3:2\]                  

    B) \[2:2\]                 

    C) \[1:2\]   

    D) \[2:1\]

    Correct Answer: C

    Solution :

    [c]
      Distilled \[{{H}_{2}}O\](No hardness, lather factor) Tap \[{{H}_{2}}O\](Temporary+ Permanent hardness Boiled \[{{H}_{2}}O\](Only permanent Hardness temporary  hardness is removed by  boiling)
    Volume of soap  solution required \[2mL\] \[17mL\] \[7mL\]
    Volume of soap effectively used       - \[17-2=15\]mL \[7-2=5\,mL\]
    (Temporary and permanent hardness) in tap \[{{H}_{2}}O=15mL\] Permanent hardness in boiled \[{{H}_{2}}O=5mL\] Temporary hardness in \[{{H}_{2}}O=15-5=10\,mL\] \[\frac{Permanent\text{ }hardness~~}{Temporary\text{ }hardness~~}=\frac{5}{10}=1:2\] Hence, answer is (3).         


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