We know that the relationship between Kc and Kp is

Kp=Kc(RT)n

What would be the value of n for the reaction?

NH4Cl(s)NH3(g)+HI(g)

(1) 1

(2) 0.5

(3) 1.5

(4) 2

Hint: ng =  number of gaseous molecules of products - number of gaseous molecules of reactants.
 
The relationship between Kc and Kp is
 
Kp=Kc(RT)n
 
where, n=(number of moles of gaseous products)-(number of moles of gaseous reactants)
 
For solide state reactant or product number of moles is constant and we did not include it.
 
For the reaction,
 
NH4Cl(s)NH3(g)+HI(g)n=2-0=2