what is the difference between  rho and sigma factor????????

sigma factor is the initiation factor that helps the RNA polymerase bind with the promoter end of the DNA strand and begins transcription.

Rho factor binds with the RNA polymerase upon reaching the termination region and help it to 'fall off' the DNA strand, so does the nascent, or prepared, RNA.

the sigma and rho factors are substances or chemicals that help intitate and terminate the transcription process but  do not take part in it directly.

Hope that helped!