Consider the following electrochemical cell at standard condition.
Au(s)ā£QH2ā,Qā£NH4āX(0.01Ā M)ā£ā£Ag+(1Ā M)ā£Ag(s)Ecellā=+0.4Ā V
The couple QH2ā/Q represents quinhydrone electrode, the half cell reaction is given below :
[Figure: p-benzoquinone (Q) +2eā+2H+ā hydroquinone (QH2ā)] EQ/QH2āāā=+0.7Ā V
[Given:EAg+/Agāā=+0.8Ā VĀ andĀ F2.303RTā=0.06Ā V]
The pKbā value of the ammonium halide salt (NH4āX) used here is __________. (nearest integer)