The number of millimoles = Molarity×Volume in mL
HCl produce one and H2SO4 produce two H+ ions respectively.
Total milimoles of H+=(600×0.01)+(400×0.01×2)=14
Thus, moles of hydrogen ion:
⇒[H+]=100014=14×10−3
⇒pH=−log[H+]=−log[14×10−3]
⇒pH=3−log14
=1.86
=186×10−2