  In the previous paper we studied the transport coefficients of Quark-Gluon
Plasma in finite temperature and finite density in vector and tensor modes. In
this paper, we extend it to the scalar modes. We work out the decoupling
problem and hydrodynamic analysis for the sound mode in charged AdS black hole
and calculate the sound velocity, the charge susceptibility and the electrical
conductivity. We find that Einstein relation among the conductivity, the
diffusion constant and the susceptibility holds exactly.
