All requirements are not given:
Assuming some values:
No of moles of HCl = 100 x 0.2 /1000 = 0.02
No of moles of NaOH = 50 x 0.250 / 1000 = 0.0125
moles HCl in excess = 0.02 - 0.0125 = 0.0075
Total volume = 150 mL
Converting mL into L= 150mL = 0.150 L
[H+] = 0.0075 / 0.150 = 0.05 M
As,
pH is the negative log of hydrogen ion concentration:
pH = - log 0.05 = 1.30
at equivalence point Concentration of hydroxyl ions is equal to Concentration of Hydrogen ions:
[OH-] = [H+] so pH = 7
