Štampana ploča ima opasnu materiju.

Because it agrees with ploča, which is a feminine singular noun.

In Serbian, adjectives must match the noun they describe in:

• gender
• number
• case

Here:

• ploča = feminine singular
• so the adjective is štampana = feminine singular

Compare:

• štampani dokument = printed document (masculine)
• štampana ploča = printed board (feminine)
• štampano pismo = printed letter/text (neuter)

Because materiju is in the accusative case.

The verb imati means to have, and its direct object usually goes in the accusative. In this sentence, materija is the thing being had/contained, so it changes form:

• materija = nominative
• materiju = accusative

So:

• Materija je opasna. = The substance is dangerous.
• Ima opasnu materiju. = It has/contains a dangerous substance.

For the same reason as materiju: the adjective must match the noun it describes.

Since materiju is:

• feminine
• singular
• accusative

the adjective must also be:

• feminine
• singular
• accusative

So:

• opasna materija = dangerous substance (nominative)
• opasnu materiju = dangerous substance (accusative)

It can mean either, depending on context.

Literally, ima means has. But in English, when talking about objects or materials, we often translate it more naturally as contains.

So this sentence could be understood as:

• The printed board has a dangerous substance.
• The printed board contains a dangerous substance.

In technical or safety-related contexts, contains may sound more natural in English.

Because Serbian does not use articles like English does.

So ploča can mean:

• a board
• the board

and materiju can mean:

• a substance
• the substance

The exact meaning depends on context.

That means Štampana ploča ima opasnu materiju could be interpreted as:

• A printed board has a dangerous substance
• The printed board has a dangerous substance

Context tells you which one is meant.

Ploča is a broad word that can mean:

• board
• plate
• panel
• sometimes even record in other contexts

In this sentence, štampana ploča most likely means some kind of printed board, and in technical language it may refer to a printed circuit board depending on context.

So the exact English translation can vary with the situation.

Not exactly.

• materija usually means substance, matter
• materijal usually means material

In many contexts they are related, but they are not always interchangeable.

Here, opasna materija sounds like:

• a dangerous substance
• a hazardous substance

That is often the more natural choice in safety or chemical contexts.

Yes. Serbian word order is more flexible than English word order because case endings show grammatical roles.

The basic order here is:

• Štampana ploča = subject
• ima = verb
• opasnu materiju = object

But other orders are possible, especially for emphasis:

• Opasnu materiju ima štampana ploča.
• Ima opasnu materiju štampana ploča.

These alternatives may sound more marked or context-dependent, but they are grammatically possible. The original order is the most neutral.

A rough English-style guide would be:

• Štampana ≈ SHTAHM-pah-nah
• ploča ≈ PLOH-chah
• ima ≈ EE-mah
• opasnu ≈ oh-PAHS-noo
• materiju ≈ mah-teh-REE-yoo

A few letter notes:

• š sounds like sh in shoe
• č sounds like ch in church
• j sounds like y in yes

It is a normal and understandable choice, but depending on context, you may also see odštampana.

Very roughly:

• štampan / štampana / štampano = printed
• odštampan / odštampana / odštampano = printed out / completed as a printed result

In many everyday contexts, štampana works perfectly well. In a technical phrase, the preferred wording may depend on the field and established terminology.