I think question is incomplete it should be mentioned here that the complete neutriluzation is going on .
For complete neutralization
Moles of OH− ions =Moles of H+ ions. ----(1)
Moles of OH− ions =2×Moles of Ba(OH)2
Moles of OH− ions =2×13.7×10−3×0.23
Moles of OH− ions =6.302 × 10−3-------(2)
From 1 and 2,
6.302 × 10−3= molarity of HBr × volume of HBr
∴ Molarity HBr= (6.302×10^-3)/25
=0.25M