Which of the following represent chemical equilibria on mixing?
a. 20 mL of 0.1 M HCl + 20 mL of 0.1 M NaOH
b. 20 mL of 0.1 M NH4OH + 20 mL of 0.1 M HCl
c. 20 mL of 0.1 M AgNO3 + 20 mL of 0.1 M KCl
d. 20 mL of 0.1 M K2CrO4 + 20 mL of 0.1 M Pb(NO3)2