Â
PKb  = -logKb
                      Â
= -log1.8*10-5
                      Â
= 4.75
    POH   = PKb +
log[NH4Cl]/[NH3]
             Â
= 4.75 + log0.2/0.5
             Â
= 4.75 -0.3979
             Â
= 4.3521
    PH  = 14-POH
           Â
= 14-4.3521Â Â = 9.6479 >>>> answer