Þetta svar kemur mér á óvart.

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Breakdown of Þetta svar kemur mér á óvart.

• mér: me
• koma á óvart: to surprise
• svar: the answer

Questions & Answers about Þetta svar kemur mér á óvart.

Why is mér in the dative case here?

The verb koma (“to come”) when used in the idiom „koma e-m á óvart“ (“to surprise someone”) requires a dative object for the person experiencing the surprise. So mér is the dative form of ég (“I”), meaning “to me.”

What is the literal, word-for-word translation of „Þetta svar kemur mér á óvart“?

Literally it reads:
“This answer comes to me on surprise.”
In smoother English: “This answer comes as a surprise to me.”

Why do we say á óvart instead of just óvart?

„á óvart“ is a set prepositional phrase.

• á is a preposition governing the dative (hence á
  • óvart).
• óvart here functions as a noun/adverbial element meaning “unexpectedness” or “surprise.”
  Without á, you’d lose the idiomatic “to surprise” sense.

Can I replace „Þetta svar“ with „Svarið“?

Yes.

• „Þetta svar“ = “this answer” (demonstrative + indefinite “answer”).
• „Svarið“ = “the answer” (definite).
  Both are grammatically correct; you’ll only change nuance (demo­strative vs. definite).