A2g  + B2g ⇌   3X2g,   ΔH=+XkJ  According to Lechatelier's principle, favourable conditions for the decomposition  of X2 are

Forward  reaction is endothermic ∴High T favours forward reaction  Since product formation involves increase in volume (no. of moles) , low pressure favours product formation.But decomposition of X2 is the backward reaction,It is favoured at  Low T and  High P