Final answer:
Clarisse McClellan is the character in 'Fahrenheit 451' known for her energy, optimism, and free spirit, signifying innocence and resistance to the repressive society.
Step-by-step explanation:
The character in Fahrenheit 451 described as having energy, optimism, and a free spirit, with a child-like innocent glow, is A) Clarisse. Clarisse McClellan is a seventeen-year-old girl who meets the protagonist, Guy Montag, and her unconventional views on life and society contrast sharply with the oppressive world in which they live. Her character embodies curiosity and love for the world around her, which sparks a change in Montag's perspective about his own life and the society he serves as a fireman. In the novel, she is a symbol of innocence and freedom, representing the potential for human connection and the beauty of the world when looking beyond the repressive state-imposed norms.