can one expect such tough words in actual GRE?

Did not know most of these words.

I thought because of the word somber, that uninhibited would be one of the answer choices. I'm confused by why wry is correct.

POE applied,, and an educated guess went successful.
uninhibited - unstoppable, out of scope
prurient - felt somewhat negative.. while we need something opposite of somber, out
dated - old? out
puritanical - something puritan? puritan is those who are abstemious. not opposite to somber, out

can someone comment on this

I never saw those words in , actually, all the official material available. mentor course included.

I cannot say NO definitely during a real exam.

However, those words to appear, the probability, is quite low

Not a good GRE question. It relies on the strength of knowing words than logical reasoning. But here we go,

If you don't know the meaning of puckish and wry, it does not matter. You can still answer this one. We need a word that is opposite of sombre and we can therefore eliminate uninhibited, prurient, dated, and puritanical.

Hence wry and puckish are the choices to be selected.

wry = using or expressing dry, mocking humor

puckish = impish, whimsical (think of Puck in Shakespeare's A Midsummer Night's Dream)

Both are not synonyms but can be considered opposite of sombre. Hence really bad for answer choices as well.