Given that 10.0 atm each of NO and O2 are introduced into a reaction vessel at room temperature. Calculate the partial pressure of each gas at equilibrium.

2NO(g)+O2 (g)---> 2NO2 (g)
Kp =4.2x1012. at. roomtemperature. To solve this question I need to find limiting reactant. So how do I figure out which is limiting reactant just from looking at the above equation?

You don't.

You are on the wrong path to the answer.

.......2NO(g) + O2(g)---> 2NO2(g)
I.......10.0....10.0........0
C.......-2p.....-p.........+2p
E.....10-2p.....10-p........2p

Substitute the E line into the Kp expression and solve for p and 2p.