moles of H+ = 10* (0.1/1000)
= 10^-3
volume of solution = 10+ 990 = 1000
conc of H+= moles of H+/Total volume of solution = 10^-3/1000 = 10^-6
pH =-log(H+) = -log(10^-6) =6
note: presence of NaCl does not change pH of soolution as pH is dependent only on concentration of proton.