0.5 moles of `N_2` gas is mixed with 0.72 moles of `O_2` gas in a 2 litre tank at 2000 K. The two gases react as : `N_2(g)+O_2(g) hArr 2NO(g), K_p=4.9xx10^(-5)` at 2000 K. The equilibrium concentration of NO(g) will be :
A. `4.2xx10^(-3) M`
B. `6.3xx10^(-3) M`
C. `2.1xx10^(-3) M`
D. `7xx10^(-3) M`