The dissociation of phosphorus pentachloride is an endothermic...

The given reaction is $\mathrm{PCl}_5(\mathrm{g}) \rightleftharpoons \mathrm{PCl}_3(\mathrm{g}) + \mathrm{Cl}_2(\mathrm{g})$ with $\Delta \mathrm{H} > 0$.

According to Le Chatelier's principle:

Since the reaction is endothermic ($\Delta \mathrm{H} > 0$), an increase in temperature will shift the equilibrium in the forward direction to absorb the added heat. Thus, high temperature favors the formation of products.

The number of gaseous moles increases from $1$ on the reactant side to $2$ on the product side. A decrease in pressure shifts the equilibrium in the direction of a greater number of gaseous moles. Thus, low pressure favors the forward reaction.

Continuous removal of a product (such as $\mathrm{PCl}_3$) decreases its concentration, which shifts the equilibrium in the forward direction to produce more products.

Therefore, low pressure, high temperature, and continuous removal of $\mathrm{PCl}_3$ will favor the maximum yield of products.

Answer: Low pressure, high temperature, and continuous removal of $\mathrm{PCl}_3$