2Bg⇌3Cl+Dg+90kJ,  Favourable conditions for the formation of ‘B’ according to Lechatelier's principle are

Forward reaction is exothermic, ΔH=−90kJIt is favoured at low temperatureForward reaction involves decrease in the moles of gaseous speciesIt is favoured at high pressureFormation of ‘B’ is backward reaction ;∴Formation of B is favoured at high T, low P