"Glee" (8 p.m., Fox):
It's a "Glee"-ful milestone as the musical drama airs its 100th episode. Joining the celebration are Gwyneth Paltrow and Kristin Chenoweth, along with original gleeks Mercedes (Amber Riley), Quinn (Dianna Agron) and Brittany (Heather Morris).
"Marvel Studios: Assembling a Universe" (8 p.m., ABC):
Calling all fanboys and girls: The special takes viewers behind the scenes and shows how the superhero sausage is made. Included: sneak peeks at upcoming films.
"Pretty Little Liars" (8 p.m., ABC Family): The title of tonight's season finale is "A Is for Answers," meaning Aria, Emily, Hanna and Spencer (Lucy Hale, Shay Mitchell, Ashley Benson, Troian Bellisario) are supposedly finally going to get the answers they've been seeking about Ali (Sasha Pieterse) and the night she disappeared. But you know how it works. The answers will probably only lead to more questions.
Also on Tuesday: