What is the coefficient for ${\mathrm{O}}_2$ when the equation ${\mathrm{NH}}_3+{\mathrm{O}}_2⟶\mathrm{NO}+{\mathrm{H}}_2\mathrm{O}$ s balanced with smallest whole number coefficients?

When the reaction is balanced with smallest whole number then it can be given as,

$4{\mathrm{NH}}_3+5{\mathrm{O}}_2⟶4\mathrm{NO}+5{\mathrm{H}}_2\mathrm{O}$

Here, coefficient of ${\mathrm{O}}_2$is 2.