Answer : The volume of NaOH stock solution used should be, 250 ml
Solution :
According to the neutralization law,
[tex]M_1V_1=M_2V_2[/tex]
where,
[tex]M_1[/tex] = molarity of NaOH solution = 0.50 M
[tex]V_1[/tex] = volume of NaOH solution = 3.0 L
[tex]M_2[/tex] = molarity of NaOH stock solution = 6.0 M
[tex]V_2[/tex] = volume of NaOH stock solution = ?
Now put all the given values in the above law, we get the volume of NaOH stock solution.
[tex](0.50M)\times (3.0L)=(6.0M)\times V_2[/tex]
[tex]V_2=0.25L=250ml[/tex] (1 L = 1000 ml)
Therefore, the volume of NaOH stock solution used should be, 250 ml