Il mobile è ingombrante: dobbiamo separarlo.

No. In this sentence, il mobile means the piece of furniture or the cabinet/unit.

For an English speaker, this is a common false friend:

• il mobile = a piece of furniture
• il cellulare / il telefonino = mobile phone / cell phone

So here Il mobile è ingombrante is about furniture, not a phone.

Il is the masculine singular definite article, meaning the.

So:

• il mobile = the piece of furniture

Italian usually uses articles more regularly than English, so il is completely normal here.

Because è means is.

This accent matters:

• è = is
• e = and

So:

• Il mobile è ingombrante = The piece of furniture is bulky
• Il mobile e ingombrante would be wrong

Ingombrante means something like bulky, cumbersome, or taking up a lot of space.

It is an adjective ending in -e, and adjectives of this type usually have:

• the same form for masculine singular and feminine singular
• a plural in -i

So:

• il mobile ingombrante
• la sedia ingombrante
• i mobili ingombranti
• le sedie ingombranti

Dobbiamo is the 1st person plural of dovere, meaning to have to / must.

So:

• devo = I have to
• devi = you have to
• deve = he/she has to
• dobbiamo = we have to
• dovete = you all have to
• devono = they have to

In the sentence:

• dobbiamo separarlo = we have to separate it

Because in Italian, modal verbs like dovere, potere, and volere are followed directly by the infinitive.

So you say:

• dobbiamo separare
• possiamo andare
• voglio mangiare

Not:

• dobbiamo a separare
• dobbiamo di separare

English uses have to + verb, but Italian just uses dovere + infinitive.

Because -lo is a direct object pronoun meaning it, and in Italian object pronouns can attach to an infinitive.

So:

• separare = to separate
• lo = it
• separarlo = to separate it

This is very common with infinitives.

It refers back to il mobile.

Since mobile is masculine singular, the pronoun is lo:

• il mobile → lo

So:

• dobbiamo separarlo = we have to separate it
• the it = the piece of furniture

Yes. That is also correct.

With a modal verb like dovere, the object pronoun can often go:

1. attached to the infinitive
   • dobbiamo separarlo
2. before the conjugated verb
   • lo dobbiamo separare

Both are grammatical. The version in your sentence is very natural.

Literally, yes, but in context it may be better understood as:

• take apart
• split up
• separate into pieces

If the furniture is too bulky, the idea is probably that it needs to be separated into parts so it can be moved more easily.

In everyday Italian, if you specifically mean dismantle furniture, smontare is also very common:

• dobbiamo smontarlo

But separarlo is understandable as given.

The colon introduces an explanation or consequence.

So the structure is roughly:

• The furniture is bulky: we have to take it apart.

It works a bit like:

• because of that
• so
• or an English colon/dash

It connects the two ideas very neatly.

Yes. Un mobile is one piece of furniture, such as a cabinet, wardrobe, or similar item.

This can be surprising for English speakers, because English often uses furniture as an uncountable noun. Italian is different here:

• un mobile = one piece of furniture
• i mobili = pieces of furniture / furniture items

You would need to change the article, adjective agreement where necessary, and the pronoun.

Examples:

• La sedia è ingombrante: dobbiamo separarla.

  • The chair is bulky: we have to separate it.

• I mobili sono ingombranti: dobbiamo separarli.

  • The pieces of furniture are bulky: we have to separate them.

• Le sedie sono ingombranti: dobbiamo separarle.

  • The chairs are bulky: we have to separate them.

Notice the pronouns:

• lo = masculine singular
• la = feminine singular
• li = masculine plural
• le = feminine plural

Roughly: seh-pah-RAHR-lo

A few useful points:

• the stress falls on -rar-: sepaRARlo
• the r is rolled or tapped in Italian
• lo is a clear final syllable, not reduced like in English

So it sounds like one smooth word: separarlo.