Questions
1: In which episode was Emma killed.
2: In which episode did Adam come back.
3: Which mutant is it who disappears.
Thanks for the help.
"Hasta la vista, baby."
Emma was "killed" between seasons. So, her death presumably occurs in the explosion / destroyed building we see in the episode "Lest He Become", but we only have confirmation that she's dead in episode 3-01, "Into The Pale Moonlight."
Adam comes back in the last episode, "The Prophecy", unless I'm mistaken. Been a while since I saw that one.
Not sure what you're referring to, but it's Adam who disappears in 3-01 (he's not a mutant, though). If you're talking about mutant powers, both Lexa and Danielle Hartman have the power to become invisible.
Hope that helps.