Hey there!
Stock solution:
Concentracion bromide = 0.128 M
initial solution in volumetric flask = 450 µl
So , moles of bromide present:
450 µl in liters :
1 µl = = 1*10⁻⁶ liters
450 * ( 1*10⁻⁶ ) = 0.00045
0.128 * 0.00045 => 57.6 * 10⁻⁶ moles
Now volume final is 25 mL , in liters : 0.025 L ou 25*10⁻³
so new bromide concentration:
57.6*10⁻⁶ / 25*10⁻³=> 2.304*10⁻³ M