L'ampolla és dins.

Because ampolla begins with a vowel. In Catalan, the singular definite article la is shortened before a vowel or silent h, becoming l'.

So:

• la casa
• l'ampolla

The noun is still feminine; only the form of the article changes.

Yes, ampolla is feminine. In this sentence you can tell because the underlying article is la, which becomes l' before a vowel.

A few related forms:

• singular: l'ampolla
• plural: les ampolles

In Catalan, ser is often used for simple location, especially with adverbs or place expressions:

• On és la Maria?
• El llibre és aquí.
• L'ampolla és dins.

This is different from Spanish, where estar is normally used for location. So for an English speaker who also knows Spanish, és here may feel surprising, but it is normal Catalan.

Here dins means inside. It is being used as an adverb, so it can stand on its own when the place is already understood from context.

For example, if everyone knows you are talking about a box, cupboard, or room, dins by itself is enough.

Yes. The sentence does not say what the bottle is inside of, because that information is assumed to be clear from the situation.

So this works like English The bottle is inside — inside the box, the house, the cupboard, etc., depending on context.

You would usually use dins de or dintre de + noun.

Examples:

• L'ampolla és dins de la capsa.
• L'ampolla és dintre de l'armari.

So:

• dins = inside
• dins de + noun = inside of something

Yes. dins and a dins are both possible. In many contexts they mean the same thing.

• L'ampolla és dins.
• L'ampolla és a dins.

Depending on the region or speaker, one may sound a bit more natural or colloquial than the other, but both are valid.

The apostrophe is not pronounced separately. It just shows that the vowel in la has disappeared.

So l'ampolla is pronounced as one unit, roughly like lam-PO-lya in many accents.

A useful point:

• the stress is on po
• ll in standard Catalan is usually a palatal sound, similar to ly

No. It only changes the form of the article in writing and pronunciation. l'ampolla still simply means the bottle.

So:

• la
  • vowel-initial feminine noun → l'

The meaning stays the same.

You can also use dintre. It is very close in meaning to dins.

So all of these are possible:

• L'ampolla és dins.
• L'ampolla és dintre.
• L'ampolla és dins de la caixa.
• L'ampolla és dintre de la caixa.

In everyday use, dins is very common and straightforward.