$\mathrm{K}_{\mathrm{c}} $$ =\frac{\left[\mathrm{N}_2\right]\left[\mathrm{O}_2\right]}{[\mathrm{NO}]^2} $

$ =\frac{3 \times 10^{-3} \times 4.2 \times 10^{-3}}{2.8 \times 10^{-3} \times 2.8 \times 10^{-3}} $

$ =1.607$

$2 \mathrm{NO}_{(\mathrm{g})} \rightleftharpoons \mathrm{N}_{2(\mathrm{~g})}+\mathrm{O}_{2(\mathrm{~g})} $

$\mathrm{t}=0 $

$0.1 \quad 0 \quad 0 $

$0.1-0.1 \alpha \quad 0.05 \alpha \quad 0.05 \alpha $

$\mathrm{K}_{\mathrm{c}}=\frac{0.05 \alpha \times 0.05 \alpha}{(0.1-0.1 \alpha)^2} $

$\mathrm{~K}_{\mathrm{c}}=\frac{0.05 \alpha \times 0.05 \alpha}{0.01(1-\alpha)^2} $

$1.607=\frac{(0.05)^2 \alpha^2}{0.01(1-\alpha)^2} $

$\frac{\alpha^2}{(1-\alpha)^2}=\frac{1.607 \times(0.1)^2}{(0.05)^2} $

$\frac{\alpha}{1-\alpha}=\frac{1.27 \times 0.1}{0.05} $

$\frac{\alpha}{1-\alpha}=2.54 $

$\alpha=2.54-2.54 \alpha $

$3.54 \alpha=2.54 $

$\alpha=\frac{2.54}{3.54}=0.717$