Solve this:

Q . The volume of water added to 500 mL, 0.5 M  NaOH so that its strength becomes 10 mg NaOH per mL is 
(1) 250 mL            (2) 500 mL
(3) 750 mL            (4) 1000 mL 
 

Dear student ,
       strength of NaOH = 10 mg / ml or 10 gm /L ; then molarity = strength / mol. mass. = 10 / 40 = 0.25 M
       now ; let x ml water is to be added in 500 ml to prepare the desired conc.of NaOH
        then from the molarity eq.  before dilution       after dilution
                                                       M1 V1          =       M2 V2
                                                     O.5 × 500     =    0.25 × (500 +x )
                on solving  ;                  1000              =  500 + x 
                                             then        x             = 500 ml (option 2)
Regards

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Hence from this you have to add 500ml of water to this solution

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