Learn Portuguese (Portugal): Ninguém mora naquele andar durante o inverno. - Nobody lives on that floor during the winter.

Since andar is a masculine noun, the ordinal numbers placed before it must also be masculine. You would say o primeiro andar (the first floor), o segundo andar (the second floor), and so on up to o décimo andar (the tenth floor).

Why do we use naquele instead of just aquele for "that"?

To say "on that" or "in that", Portuguese combines the preposition em (in/on/at) with the word aquele (that) to make the contraction naquele. Because andar is masculine and singular, the contraction stays in its masculine singular form.

Does ninguém (nobody) always take the singular verb form like mora?

Yes! Just like in English where we say "nobody lives" (treating it as a single unit), Portuguese indefinite pronouns like ninguém (nobody), alguém (somebody), and tudo (everything) always use the third-person singular verb conjugation. This is the exact same form you use for ele, ela, or você.

Why is there an o before inverno? English just says "during winter" here.