Final answer:
The word "Just" in the given sentence should not be capitalized unless following title case conventions for song titles. The correct song title should be either "Just Dance" or "Just dance" depending on the capitalization style chosen. Italicization of both words is acceptable and used for titles.
Step-by-step explanation:
The word "Just" in the sentence "The name of that song is "Just dance."" is incorrectly capitalized. In the context of a song title, both significant words should be capitalized.
The corrected song title should be "Just Dance" if referring to the common convention where most words in titles are capitalized. But if you are referring to sentence-style capitalization which is sometimes used in reference works, then the word "dance" should remain lowercased unless it is the first word of the sentence or title.
As for italicizing, song titles are often italicized for emphasis or to show that it is a title of a work, so it would be correct to italicize both words.
When addressing problems with mixed sentences just like in Mixed Sentence 1, it's essential to provide a clear subject and verb without extraneous interruptions. The correct revision might be: "Learning to ballroom dance has shown increased agility and a longer life expectancy." Here, the superfluous "it" is removed to ensure the subject directly connects with the verb.