Non c’è posto nel mio zaino.

Because c’è means there is.

It comes from ci + è:

• ci = there
• è = is

So:

• C’è posto = There is room / space
• Non c’è posto = There isn’t room / space

Using just è would mean only is, which would not express there is.

Posto literally means place, but in this sentence it is used in the sense of room or space.

So Non c’è posto is a very natural way to say:

• There’s no room
• There’s no space

Depending on context, posto can also mean:

• a place
• a seat
• a spot

For example:

• C’è un posto libero? = Is there a free seat/spot?

In Italian, non normally goes directly before the verb to make it negative.

So:

• C’è posto = There is room
• Non c’è posto = There is not room

This is the standard way to form negation in Italian.

Because nel is the contracted form of in + il.

• in = in
• il = the
• in + il = nel

So:

• nel mio zaino = in my backpack

Italian very often combines prepositions and definite articles this way. For example:

• a + il = al
• di + il = del
• su + il = sul

Because Italian usually uses the definite article with possessive adjectives.

So Italian typically says:

• il mio zaino = literally the my backpack

After a preposition, the article is still there, but it combines with the preposition:

• in il mio zaino becomes nel mio zaino

This is very normal in Italian:

• la mia macchina = my car
• nel mio zaino = in my backpack

The apostrophe shows that ci becomes c’ before è.

So:

• ci è becomes c’è

This is just the standard written form. It is very common:

• c’è = there is
• c’erano = there were

You should learn c’è as a fixed, very common expression.

Yes, absolutely.

Spazio also means space, and in many situations it works very well:

• Non c’è spazio nel mio zaino = There’s no space in my backpack

The difference is small:

• posto often sounds like room/space available
• spazio can sound a bit more literal or physical

In everyday speech, both can be correct depending on context.

Because zaino is a masculine noun in Italian.

You can see this from:

• il zaino → actually lo zaino
• mio zaino
• nel mio zaino

A useful detail: zaino takes lo in the singular because it begins with z:

• lo zaino = the backpack
• gli zaini = the backpacks

But after in + lo, you get:

• nello zaino = in the backpack

In your sentence, though, it is my backpack, so the phrase is:

• nel mio zaino

Because the article used before a possessive can change.

With zaino alone, you say:

• lo zaino

But with a possessive adjective like mio, Italian normally uses:

• il mio zaino

So:

• in + il mio zaino = nel mio zaino

That is why nel mio zaino is correct, not nello mio zaino.

This is a pattern you will see often:

• il mio studente
• il mio zio
• il mio zaino

Yes, but the given order is the most natural neutral one.

Standard:

• Non c’è posto nel mio zaino.

You could also hear:

• Nel mio zaino non c’è posto.

This version puts more emphasis on nel mio zaino.

Both are correct, but the original sentence is the most straightforward everyday phrasing.

It is pronounced roughly like cheh in English spelling, but with a clear Italian ch sound as in check, not like English sh.

So:

• c’è sounds approximately like cheh

Also remember:

• the è is an open e sound
• the stress is on that syllable, since it is only one syllable

If you say the whole sentence naturally:

• Non c’è posto nel mio zaino

the c’è is short and very common in speech.