O tapete da sala está sujo; os convidados ficariam mais confortáveis se estivesse limpo.

Because da is the contraction of de + a.

• de = of / from
• a = the (feminine singular)

So:

• o tapete da sala = the carpet/rug of the room
• literally: the rug of the room

Portuguese uses these contractions very often:

• de + o = do
• de + a = da
• de + os = dos
• de + as = das

So de a sala would sound wrong in normal Portuguese.

In Brazilian Portuguese, sala often means the living room or sitting room, depending on context.

So o tapete da sala usually means the living-room rug/carpet or the rug in the living room.

A learner may first think sala just means room, and it can, but in everyday Brazilian usage it very often refers specifically to the main living area of a home.

Because the two parts talk about different kinds of situations:

• está sujo = a real, current fact
• estivesse limpo = a hypothetical situation

So:

• O tapete da sala está sujo = The living-room rug is dirty
  This is presented as true now.

• se estivesse limpo = if it were clean
  This is imagined, not real.

Portuguese, like English, changes the verb form when moving from a real statement to a hypothetical one.

Estivesse is the imperfect subjunctive of estar.

This form is very commonly used after se when talking about hypothetical or unreal situations in the present or future.

A very common pattern is:

• se + imperfect subjunctive, then
• conditional

That is exactly what you have here:

• se estivesse limpo = if it were clean
• ficariam mais confortáveis = they would be / would feel more comfortable

So the sentence follows a classic Portuguese hypothetical structure.

Because ficariam is the conditional, and the sentence is hypothetical.

Compare:

• ficam = they become / they get / they are (present)
• ficarão = they will become / will be (future)
• ficariam = they would become / would be (conditional)

Here the sentence means:

• the guests would be more comfortable if the rug were clean

That would idea is exactly why Portuguese uses ficariam.

It refers back to o tapete da sala.

Portuguese often leaves out pronouns or repeated subjects when the meaning is clear from context. So:

• se estivesse limpo literally means if [it] were clean
• the understood it is the rug

You could make it explicit:

• se ele estivesse limpo

But that is usually unnecessary here, because the reference is already obvious.

Because estar is used for a state or condition, while ser is used more for essential identity, classification, or sometimes the passive voice.

Here, limpo means clean as a condition of the rug:

• o tapete está limpo = the rug is clean
• o tapete está sujo = the rug is dirty

If you used ser, it would not sound natural for this meaning.

A useful contrast:

• estar limpo = to be clean
• ser limpo = to be a clean person/thing by nature, or in some contexts to be cleaned in a passive-like sense, depending on structure

For everyday descriptions of cleanliness, use estar.

Yes, estariam mais confortáveis is possible, but ficariam mais confortáveis is very natural here.

The difference is subtle:

• ficar confortável often suggests ending up feeling more comfortable
• estar confortável focuses more directly on being comfortable

So:

• os convidados ficariam mais confortáveis = the guests would feel / would be more comfortable
• os convidados estariam mais confortáveis = the guests would be more comfortable

Both work, but ficariam sounds very natural when talking about how a situation would affect someone’s comfort.

Because the adjective agrees with os convidados, which is plural.

Agreement in Portuguese is important:

• o convidado está confortável = singular masculine
• os convidados estão confortáveis = plural masculine
• a convidada está confortável = singular feminine
• as convidadas estão confortáveis = plural feminine

In your sentence, the people being described are os convidados, so the adjective must be plural:

• confortáveis

In Portuguese, the masculine plural is used for:

• a group of men, or
• a mixed group of men and women, or
• a group whose gender is unspecified

So os convidados can mean:

• the male guests, or
• the guests in general

If the group were all female, you would say:

• as convidadas

Yes, absolutely.

That version is often easier for learners because it states the subject again:

• Se o tapete estivesse limpo, os convidados ficariam mais confortáveis.

It means the same thing. The original version simply avoids repeating o tapete because it is already understood.

So the two versions are both correct:

• O tapete da sala está sujo; os convidados ficariam mais confortáveis se estivesse limpo.
• O tapete da sala está sujo; os convidados ficariam mais confortáveis se o tapete estivesse limpo.

The shorter version is more natural once the reference is clear.

It means more comfortable than they would be now / in the current situation.

The comparison is implicit. The rug is dirty now, so the idea is:

• in the current situation, the guests are less comfortable
• if the rug were clean, they would be more comfortable

Portuguese often leaves that comparison unstated because it is obvious from context, just like English does.

The semicolon links two closely related clauses:

• O tapete da sala está sujo
• os convidados ficariam mais confortáveis se estivesse limpo

It shows a stronger break than a comma, but a weaker break than a period.

In English, the same punctuation choice is possible:

• The living-room rug is dirty; the guests would be more comfortable if it were clean.

A period would also be possible. The semicolon just emphasizes that the second idea is closely connected to the first.

Not exactly in all contexts.

In Brazilian Portuguese:

• tapete usually means a rug or mat
• carpete often refers to wall-to-wall carpeting

But real usage can vary, and sometimes English translations use carpet for tapete depending on context.

So in this sentence, tapete da sala is most naturally understood as a rug in the living room.