The equilibrium constant for the chemical equation is kp = 5.23 at 191 °c. calculate the value of the kc for the reaction at 191 °c.

To convert from Kp to Kc, you need this formula---> Kp= Kc (RT)^Δn, where Δn= gas moles of product- gas moles of reactants. since you did not give a reaction formula, I can't calculate Δn. but all once you find it out. just plug it. 

Kp= Kc (RT)^Δn> Kc= Kp/[(RT)^Δn]
 Kp= 5.23
R= 0.0821
T= 191 C= 464 K
Δn= ?

Kc= 5.23/ (0.0821 x 464)^Δn= ???