"Is this country's coast short?"
Translation:هَل ساحِل هٰذا الْبَلَد قَصير؟
Should the question be: Is the coast of this country short?
I answered (incorrecly): Hal hadha al-balad saaHil QaSeer?
Is this not correct in Arabic?
It can be so and it's no different than the original English sentence stated here (I guess Duolingo still doesn't recognize this?).
Your sentence here would translate to: Is this country a short coast?
The word ساحل (saaHil) should come before (hadha al-balad) and as such the phrase will be (coast of this country) ساحل هذا البلد.