Is the word nas the same in Brazilian and European Portuguese?

Yes.

The word "nas" is a contraction of the preposition em (in) and the feminine plural definite article as (the). There are no differences in meaning, spelling, or grammar between Brazilian and Continental Portuguese. The only difference is pronunciation: in most Brazilian accents, the "s" is pronounced as a voiceless alveolar fricative [s], whereas in Continental Portuguese, the "s" at the end of a syllable is typically pronounced as a voiceless postalveolar fricative [ʃ], sounding like "sh" in "shoe."

Brazilian Portuguese

1. As crianças estão nas escolas. (The children are in the schools.)
2. As canetas estão nas mochilas. (The pens are in the backpacks.)
3. Há muitos erros nas respostas. (There are many errors in the answers.)
4. As fotos estão nas redes sociais. (The photos are on social media.)
5. Encontrei moedas nas calças. (I found coins in the pants.)

Continental Portuguese

1. As crianças estão nas escolas. (The children are in the schools.)
2. As canetas estão nas malas. (The pens are in the bags.)
3. Há muitos erros nas respostas. (There are many errors in the answers.)
4. As fotos estão nas redes. (The photos are on the networks/social media.)
5. Encontrei moedas nas calças. (I found coins in the pants.)