Although HCl is an stron acid but HBrO is not . Ka of HBrO is
2*10^-9 M
0.18 M HCl gives 0.18 H+. Now lets find net concentration of H+
whe HBrO is also there.
                               Â
HBrO ---->Â Â H+Â Â + BrO-
initial:Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â
0.25 0.18 0
final:Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â
0.25-x          Â
0.18+x  x
Ka = [H+][BrO-] / [HBrO]
2*10^-9 = (0.18+x)*x / (0.25-x)
Since Ka is very small, x willl be very small and it can be
ignored as compared to 0.25 and 0.18,
so above expression becomes:
2*10^-9 = (0.18)*x / (0.25)
x = 2.77*10^-9 M
[H+] = 0.18 M + 2.77*10^-9 M = 0.18 M
pH = -log [H+]
  = -log (0.18)
= 0.744
Answer: 0.744
