First calculate how much moles of NaOH is there in a 1L of 0.75M:
[tex]1L*0.75M =0.75moles[/tex]
Now, find the moles of x liters of 2.5M NaOH:
[tex]x*2.5M = 2.5x\,moles[/tex]
Equating the two equations:
[tex]0.75 = 2.5x[/tex]
[tex]x=0.3L[/tex]
We need 0.3L of 2.5M NaOH to make a 0.75M of NaOH solution.
