The molar conductivity of 0.009 M aqueous solution of a weak acid (HA) is 0.005 S m² mol⁻¹ aned the limiting molar conductivity of HA is 0.05 S m² mol⁻¹ at 298 K. Assuming activity coefficients to be unity, the acid dissociat ion constant (Ka) of HA at this temperature is:

a) d-d transit ion
b) Transit ion in K⁺ ion
c) Ligand to metal charge transfer
d) Metal to ligand charge transfer