"El pantalón es amarillo."
Translation:The pants are yellow.
Not sure why you got downvotes. That seems to make sense. In American Vernacular, we just add leg to pant to clarify.
It's the same in English, pants can be the one pair, or multiple just like Spanish. Any number of pairs can be thrown in for clarification, but this is only required in formal English.
Yes, that is correct. The verb 'es' is used when the subject is singular. The translation for 'the pants are yellow' is "los pantalones son amarillos". The Duolingo sentence is grammatically incorrect, and has caused a lot of confusion. The sentence should be deleted from the Duolingo lessons.
Not quite. Pants is a rare noun that does not exist in the singular. It's rare but it does happen. Maybe the word pant (as in the clothing article) once existed as a singular noun, but not anymore. The same quirk is true for billiards, measels, annals, victuals, etc. Not every plural has a corresponding singular. (Think of it this way... if pants could be singular, then the sentence "that pants is nice" would be correct)