Your tool of choice here will be the equation
$color(blue)(ul(color(black)(K_p = K_c * (RT)^(Deltan))))$
Here
$K_p$ is the equilibrium constant in terms of partial pressures$K_c$ is the equilibrium constant in terms of concentrations$R$ is the universal gas constant, equal to$0.0821 quad ("atm" * "L")/("mol" * "K")$ $T$ is the absolute temperature at which the reaction takes place$Deltan$ is the difference between the number of moles of gaseous products and the number of moles of gaseous reactants
Now, your reaction takes place at
$T = 1000^@"C" + 273.15 = "1273.15 K"$
Notice that for every
This means that you have
$Deltan = color(white)(overbrace(color(black)(" 2 "))^(color(blue)("moles of ammonia")) " "color(black)(-)" " overbrace(color(black)((" 1 + 3 ")))^(color(blue)("moles of reactants"))$
$Deltan = - 2$
Rearrange the equation to solve for
$K_c = K_p/((RT)^(Deltan)$
Plug in your values to find--since you didn't provide any units for
$K_c = (2.4 * 10^(-3))/(0.0821 * 1273.15)^(-2) = color(darkgreen)(ul(color(black)(26)))$
The answer is rounded to two , the number of sig figs you have for