The resistance of a $0.1 \, M$ weak acid HA in a conductivity cell is $2 \times 10^{3} \, \Omega$. The cell constant is $0.78 \, \text{cm}^{-1}$ and $\lambda_{m}^{\circ}$ of acid HA is $390 \, S\, cm^{2}\, mol^{-1}$. The $pH$ of the solution is