Final answer:
Buck's strength, perseverance, leadership, and adaptability impress Francois and Perrault, as evidenced by his rise to lead the sled team and performance under difficult conditions.
Step-by-step explanation:
The qualities of Buck that are most impressive to Francois and Perrault in 'The Call of the Wild' are Buck's strength, perseverance, leadership, and adaptability. The evidence from the text highlighting these qualities includes instances where Buck takes on leadership of the sled team, enduring harsh conditions, and proving his value as a superior sled dog.
For example, Buck's leadership is evident when he fights and overcomes the lead dog Spitz, taking over as the leader of the team. His adaptability is shown in how he quickly learns the ways of the North and survives under difficult circumstances. Perrault and Francois specifically praise Buck's ability and they are shown to be very proud of his accomplishments, trusting him to lead their sled dog team through the perilous Yukon territory effectively.
In summary, Buck's impressive traits to his handlers are evident in the text and are centered around his strength, leadership, and adaptability. These not only ensure the success of the sled team but also carve Buck's place as a leader among the dogs.