El mosquetón está en la cinta exprés.

Because this sentence is talking about location: where the carabiner is.

In Spanish, estar is normally used for where something or someone is located:

• El mosquetón está en la cinta exprés. = The carabiner is in/on the quickdraw.
• La mochila está en el suelo. = The backpack is on the floor.

Using ser here would sound wrong, because ser is used for identity, classification, origin, and other more permanent-type descriptions, not physical location.

So a good rule is:

• ser = what something is
• estar = where something is / how something is

El is the masculine singular definite article, meaning the.

You use it because mosquetón is a masculine singular noun:

• el mosquetón = the carabiner

In Spanish, nouns usually need an article more often than in English, especially in simple descriptive sentences like this one.

Compare:

• El mosquetón está en la cinta exprés.
• La cuerda está tensa.

Here, el tells you that we are talking about a specific carabiner, not just carabiners in general.

Because grammatical gender in Spanish is something you usually have to learn with the noun itself. The ending can give you clues, but it does not always work like English speakers expect.

In this case:

• mosquetón is masculine
• so it takes el

Many nouns ending in -ón are masculine:

• el botón
• el pantalón
• el corazón
• el mosquetón

So it is best to learn the word as a chunk:

• el mosquetón

In climbing Spanish, cinta exprés is the usual term for a quickdraw.

Literally:

• cinta = strap / sling / tape
• exprés = express / quick

But you should treat cinta exprés as a fixed climbing term, not as a word-for-word phrase you need to translate literally every time.

So:

• la cinta exprés = the quickdraw

In real climbing usage, Spanish speakers may also shorten it and just say:

• la exprés

For example:

• Pásame una exprés. = Pass me a quickdraw.

Because the main noun is cinta, and cinta is feminine:

• la cinta
• la cinta exprés

The article agrees with the main noun, not with the second word.

So:

• el mosquetón = masculine
• la cinta exprés = feminine

This is very common in Spanish noun phrases.

Here en means something like in, on, or attached to, depending on the context.

Spanish en is broader than English in. It is often used where English would choose either in or on.

So in this sentence:

• El mosquetón está en la cinta exprés.

the idea is that the carabiner is on / in / attached to the quickdraw.

Even if English might prefer on the quickdraw, Spanish naturally uses en.

This is very normal:

• en la mesa = on the table
• en la mochila = in the backpack
• en la pared = on the wall

So do not try to match en to only one English preposition.

Because in Spanish, only two article contractions exist:

• a + el = al
• de + el = del

There is no contraction with en.

So:

• en el mosquetón
• en la cinta exprés
• en los dedos
• en las vías

All of these stay separate.

That is why en la remains en la, not a single word.

The accent mark in está shows where the stress goes and also distinguishes it from other forms.

• está = he/she/it is or you are (formal)
• esta without an accent is usually a demonstrative determiner: this

Examples:

• El mosquetón está aquí. = The carabiner is here.
• Esta cinta exprés es nueva. = This quickdraw is new.

So the accent is important both for pronunciation and for meaning.

Because exprés is stressed on the last syllable, and Spanish spelling marks that stress with an accent in this word.

So it is pronounced roughly like:

• ex-PRÉS

The accent helps show the correct stress pattern.

Also, in climbing vocabulary, exprés is commonly written with the accent in Spain:

• cinta exprés
• una exprés

Yes, in cinta exprés, exprés is functioning like an adjective or fixed modifier, and it is generally invariable here.

That means it does not change for gender:

• la cinta exprés

And in standard usage it often stays the same in the plural too:

• las cintas exprés

So unlike many adjectives, you do not usually make it expresa or expreses in this climbing term.

It is best to learn the full expression as fixed vocabulary:

• singular: la cinta exprés
• plural: las cintas exprés

Yes, but the original order is the most neutral and natural.

Normal Spanish word order here is:

• El mosquetón está en la cinta exprés.

You could change the order for emphasis, for example:

• En la cinta exprés está el mosquetón.

But that sounds more marked or literary, and it would usually only be used if you want to emphasize where it is.

For a learner, the standard pattern is the one to remember:

• subject + estar + location

You would change the article, noun, and verb to match the plural:

• Los mosquetones están en las cintas exprés.

Breakdown:

• el → los
• mosquetón → mosquetones
• está → están
• la → las
• cinta → cintas
• exprés stays exprés

So the full plural is:

• Los mosquetones están en las cintas exprés.

In Spain Spanish, it is pronounced approximately:

• mo-ske-TÓN

The stress is on the last syllable, which is why it has the accent mark.

A rough English-friendly guide would be:

• mos-keh-TONE

Also remember that in Spain Spanish:

• qu before e sounds like a hard k
• the final -ón is strongly stressed

So the key thing is the final stress:

• mosquetón
• not MOS-que-ton