Assume that you have 15ml of 2.5M potassium hydroxide but only have concentrated bottle of 16M strength. How would you obtain this

Answer 1

Do you mean you hav 16M KOH but you need 15 mL of 2.5M? Then
c1v1 = c2v2
2.5*15 = 16*v2
v2 = ?
You want (2.5*15/16) mL of the 16 M stuff and add water to a total of 15 mL.