Answer
$$K_p = 5.8 \times 10^{5} \space atm^{-2}$$
Work Step by Step
1. $T(K) = 25 + 273 = 298$
2. $\Delta n = 2 - 3 - 1 = -2$
3. $$K_p = K_c \times RT^{\Delta n} = (3.5 \times 10^8) \times (0.0821 \space L \space atm \space mol^{-1} \space K^{-1} \times 298 \space K)^{-2}$$
$$K_p = 5.8 \times 10^{5} \space atm^{-2}$$
