Answer:
Kc ≅ 100 (1 sig. fig.)
Explanation:
       2NH₃(g)    ⇄    N₂(g)  +  3H₂(g)
C(i) Â Â Â Â 3.00 mol/L Â Â Â Â Â Â 0 Â Â Â Â Â Â Â Â 0
ΔC       -2x            +x        +3x
C(eq)   0.600 mol/L       x         3x
3.00 - 2x = 0.600 Â => Â x = 3.00 - 0.600/2 = 1.2 mole/L
At equilibrium Kc = [N₂][H₂]³/[NH₃]² = (x)(3x)³/(3·1.2)² = (1.2)(3.6)³/(0.600)² = 155.52 (calculator)
Rounds to 1 sig. fig. based on given 3.00 moles NH₃(g)' Kc ≅ 100.