Final answer:
Napoleon's motivation for blaming Snowball for the windmill's destruction is to undermine his rival and maintain his power over the farm.
Step-by-step explanation:
The best inference about Napoleon’s motivation for blaming Snowball for destroying the windmill is that Napoleon wants to undermine Snowball and maintain control of the farm. This assertion is drawn from the fact that Napoleon is characterized as a power-hungry leader who is not above using deceit to maintain his authority. By accusing Snowball, he eliminates a potential rival and deflects any blame from himself, thereby solidifying his control over the other animals. This tactic is reflective of his tendency to manipulate situations and people to his advantage, even if this involves sacrificing honesty or the welfare of others.