X = ?

X = 24th letter of the alphabet    X = Roman Numeral     X = Kiss     X = Strike
X = Multiplication    X = Female Chromosome     X = Marks the Spot     X = Life
X = MDMA     X = Straight Edge     X = Unnamed Factor    X = Planet
X = Christ     X = Signature     X = Treasure    X = Film Rating    X = Comet
X = Reactance     X = Generation X     X = Infantry     X = Unknown Variable
X = Frequency Band     X = Size    X = Death     X= Magnification

For Me X = Kiss.