The reaction 2NO(g)+O2(g)⇌2NO2(g) is of first order. If volume of reaction vessel is reduced to ⅓, the rate of reaction would be

For following reaction, 2NO(g)+O2(g)→2NO2(g)When the volume of vessel change into 13, then concentration of reactant become three times (∵ cα1v)The rate of reaction for first order reaction ∝ concentration. So rate of reaction will increases three times.