Learn Hardcore Indonesian: Dia memeriksa cairan di laboratorium kecil itu. - He/She examines the liquid in that small laboratory.

Dia is a third‑person singular pronoun that can mean he, she, or even they (referring to one person) depending on context.
Indonesian pronouns usually do not mark gender, so you figure out whether it’s “he” or “she” from the surrounding context or from previous sentences.

How can I tell that memeriksa is in the past tense (“checked”)?

Indonesian verbs, including memeriksa, do not change form for tense. Memeriksa simply means to examine / to check.

The time is understood from:

Context: a previous sentence like Tadi pagi dia memeriksa… (This morning he/she examined…)
Time words: tadi, kemarin, sudah, sedang, akan, etc.

So dia memeriksa cairan… can mean “he/she checks the liquid”, “he/she is checking the liquid”, or “he/she checked the liquid” depending on the context given elsewhere.

What is the base word of memeriksa, and what does the prefix me- do here?

The base word is periksa, meaning check / examine.

When you add the prefix me- to periksa, you get memeriksa, which is a verb meaning to examine / to check.

The prefix me- (often with some spelling changes) typically turns a base word into an active verb, usually translated as “to do X” in English.

Is there any difference between memeriksa and something like mengecek or cek?

Yes, there are nuance and style differences:

Memeriksa – more formal / standard; often implies a more detailed or systematic examination (e.g. checking lab samples, checking a patient, checking documents).
Mengecek – a more colloquial form from the English check; very common in speech and informal writing.
Cek (verb) – very informal, spoken; often used like “to check” in casual conversation.

In a sentence about a lab, memeriksa sounds natural and slightly more formal, which fits the context of scientific work.

What does cairan mean, and how is it different from air?

Cairan means liquid in a general or technical sense—any substance in liquid form.
Air (pronounced like “ah‑eer”) means water specifically.

So:

cairan kimia = chemical liquid
air minum = drinking water

In a lab context, cairan is used because you may be dealing with various liquids, not just water.

Is cairan countable? Do I need something like “a” or “some” liquid in Indonesian?

Indonesian does not use articles like a/an/the, and many nouns, including cairan, can be countable or uncountable depending on context.

If you want to be specific, you can add a classifier or a description:

sejumlah cairan – some / an amount of liquid
tiga jenis cairan – three types of liquid
botol cairan itu – that bottle of liquid

In the sentence dia memeriksa cairan di laboratorium kecil itu, cairan is just “the liquid” / “some liquid” understood from context, with no article needed.

Why is it di laboratorium kecil itu and not di kecil laboratorium itu? What is the word order rule?

In Indonesian, the usual order is:

NOUN + ADJECTIVE + DEMONSTRATIVE (ini/itu)

So:

laboratorium (noun)
kecil (adjective: small)
itu (demonstrative: that)

→ laboratorium kecil itu = that small laboratory

Putting kecil before laboratorium (like English “small laboratory”) is not standard Indonesian. Adjectives normally come after the noun.

What exactly does itu do in laboratorium kecil itu? Is it the same as “the” or “that”?

Itu is a demonstrative that usually means that (as opposed to ini = this).

However, Indonesian doesn’t have a direct equivalent of the English article “the”. In practice:

laboratorium kecil = a small laboratory or small laboratories (general, non‑specific)
laboratorium kecil itu = that small laboratory, or the small laboratory (already known in context)

So itu both points to something specific and often corresponds to English that/the (specific one we talked about).

Why is the preposition di used with laboratorium here? Could we use pada instead?

Di is the standard preposition for physical location: in / at / on.

di laboratorium kecil itu = in/at that small laboratory

Pada is more formal and is typically used with abstract locations, time expressions, or recipients (on, upon, to):

pada hari Senin – on Monday
pada kesempatan ini – on this occasion
berpengaruh pada hasil – affects the result

Using pada laboratorium kecil itu would sound unnatural for a simple physical location; di is the correct choice.

Can this sentence also mean “He/She is examining the liquid in that small laboratory” (progressive aspect)?

Yes. Indonesian does not mark aspect with verb endings, so dia memeriksa… can mean:

He/She examines… (habitual)
He/She is examining… (right now)
He/She examined… (past)

If you want to make the progressive aspect very clear, you can add sedang:

Dia sedang memeriksa cairan di laboratorium kecil itu.
= He/She is (currently) examining the liquid in that small laboratory.

If I want to emphasize that it was done in the past, what could I add to this sentence?

You can add time markers or aspect markers, for example:

Tadi pagi dia memeriksa cairan di laboratorium kecil itu.
– This morning he/she examined the liquid in that small laboratory.
Kemarin dia memeriksa cairan di laboratorium kecil itu.
– Yesterday he/she examined the liquid in that small laboratory.
Dia sudah memeriksa cairan di laboratorium kecil itu.
– He/She has already examined the liquid in that small laboratory.

Words like tadi, kemarin, sudah, tadi pagi make the past time clear.

Could I drop dia and just say memeriksa cairan di laboratorium kecil itu?

Grammatically, you can drop dia, but it changes the feel of the sentence. Without dia:

Memeriksa cairan di laboratorium kecil itu.

This sounds like:

A fragment or note (e.g. in a lab procedure: “(Someone) examines the liquid in that small lab.”)
A command or instruction (depending on context): “(You) examine the liquid in that small lab.”

For a clear, complete sentence with a specific subject, you usually keep dia.

Is there any difference in meaning or politeness between dia and ia in this sentence?

Both dia and ia can mean he/she, but their typical usage is different:

Dia – most common in spoken Indonesian and neutral written style.
Ia – more common in formal or literary writing, usually not used after prepositions or at the beginning of a paragraph in spoken style.

You could say Ia memeriksa cairan di laboratorium kecil itu in formal writing, and the meaning is the same. In everyday speech, dia is more natural.