La muestra está en el laboratorio.

La is the feminine singular definite article, equivalent to the.

It matches muestra, which is a feminine singular noun. In Spanish, articles agree with the noun in gender and number:

• la muestra = the sample
• las muestras = the samples

So la is there because the noun is one feminine thing.

Spanish usually uses estar for location, so está en el laboratorio is the normal way to say that something is in a place.

A very useful rule is:

• ser = what something is, identity, classification, origin, etc.
• estar = where something is, or how it is

So for physical location, Spanish normally chooses estar.

One important exception: events are often located with ser. But for an object like la muestra, estar is correct.

The accent mark shows the correct stress: es-TÁ.

It also helps distinguish it from esta, which can mean this in the feminine form:

• esta muestra = this sample
• está en el laboratorio = is in the laboratory

So the accent is both a pronunciation guide and a spelling distinction.

Está is the third-person singular present form of estar.

That means it can mean:

• he/she/it is
• you are in the formal singular sense (usted)

In this sentence, it matches la muestra, which is singular, so está means it is.

Yes, muestra is a feminine noun, so it takes feminine articles and adjectives:

• la muestra
• una muestra
• la muestra pequeña

The biological or scientific object itself does not need to be feminine in real life. Grammatical gender is just part of how the noun behaves in Spanish.

En is the normal preposition for in, inside, at, or on, depending on context.

Here it is used to express location in a place:

• en el laboratorio
• en la oficina
• en casa

So en is the natural choice for saying where the sample is.

In normal Spanish, en el laboratorio is the natural form because you are referring to a specific place: the laboratory.

Saying en laboratorio without the article is not the normal everyday way to express simple location. In some technical or specialised contexts, article use can vary, but for a basic sentence about where something is, en el laboratorio is the standard choice.

Because in Spanish, only two common contractions are used in standard grammar:

• a + el = al
• de + el = del

But:

• en + el stays en el

So en el laboratorio is correct, not a contraction.

Yes. La muestra está en el laboratorio is the most neutral word order.

But Spanish can change word order for emphasis:

• En el laboratorio está la muestra = puts more focus on the location or contrasts it with another place

The original sentence is the best basic version, but other orders are possible in context.

Yes, if the context already makes it clear what you are talking about.

For example:

• ¿Dónde está la muestra?
• Está en el laboratorio.

Spanish often leaves out subjects when they are understood from context. In this case, the omitted subject would be understood as the sample.

A simple pronunciation guide is:

la MWES-tra es-TA en el la-bo-ra-TO-rio

A few points:

• muestra begins with a mw sound: MWES-tra
• está is stressed on the last syllable: es-TÁ
• laboratorio is stressed on TO: la-bo-ra-TO-rio
• In natural speech, está en often flows together smoothly

If you want to sound more natural, make sure the stress is clear in está and laboratorio.

Not always. Muestra can have several meanings depending on context, such as sample, specimen, or even display/showing in some situations.

In this sentence, because of en el laboratorio, the scientific or technical meaning is the obvious one. So context tells you which meaning is intended.

Yes, laboratorio is a masculine noun, so it takes el:

• el laboratorio
• un laboratorio

Many nouns ending in -o are masculine, though there are exceptions in Spanish. Here, the standard pattern works: laboratorio is masculine.