The sentence in the excerpt that shows a mocking tone is:
Like he could ever be an astronaut!
Explanation:
To mock means to make fun of something or someone in a derisive, cruel manner. Notice how the sentence "Like he could ever be an astronaut!" mocks the sentence that came before it. It is, in a cruel, sarcastic way, refuting the possibility of Jason becoming an astronaut like he used to dream of. We can easily hear the tone in which the sentence would be spoken in our minds - a laughing, ironic tone.
