nel/sul vs in
I'm a bit confused with when nel becomes just in and even on the becomes in e.g. (la cena e in tavola - dinner is on the table). Why wouldn't it be 'la cena e sulla tavola'. Another one is 'non abbiamo una scala in cucina' I'm unsure when nel shouldn't be used. It would be great if someone could clear this up for me
non abbiamo una scala in cucina
Parts of one's own house (or of a house in general) take the simple preposition in.
Rules, examples and exceptions can be found here:
la cena e in tavola
Beware that e and è are different words, with a different meaning.
In the expression in tavola, the table is dealt with as a generic place, rather than as a specific piece of furniture.
Several other nouns can be dealt with in the same way, always using the simple preposition in. Some common ones are:
in tasca = in the pocket
in borsa = in the handbag
in testa = on one's head
in copertina = on the cover
in prima pagina = on the first page
Also a long list of common places take the simple preposition in (see https://www.duolingo.com/comment/17402953).
When using in (rather than nel, nello, nella) a place is always mentioned in an abstract way. For instance:
Vado in banca. = I am going to the bank.
gives information about the type of place (bank), but not about which bank, nor which branch office it is.
Ha una penna in tasca. = He/She has a pen in the pocket.
does not tell us which pocket the pen is in, but only the type of place (pocket). Further details can be often understood from the context.
So La cena è in tavola tells us that the dinner has been served → it is "on (the) table". The table may likely be the speaker's usual dining table, but it may also be any other table in the house. What counts most in conveying this piece of information is the type of place (table).