Questo materiale è puro.

Because materiale is a masculine singular noun.

In Italian, demonstratives like questo / questa / questi / queste must agree with the noun they describe:

• questo = masculine singular
• questa = feminine singular
• questi = masculine plural
• queste = feminine plural

So:

• questo materiale = this material
• questa sostanza = this substance

Even though materiale ends in -e, it is still masculine.

You usually learn the gender together with the noun. Italian nouns ending in -e can be either masculine or feminine, so the ending alone does not always tell you.

Here, materiale is masculine, which you can see from the agreement:

• questo materiale
• è puro

Both questo and puro are masculine singular, so they confirm the gender of materiale.

È is the third-person singular form of essere = to be.

• è = is

The accent is important because it distinguishes è from e:

• è = is
• e = and

So:

• Questo materiale è puro = This material is pure
• Questo materiale e puro would be incorrect

Because adjectives in Italian must agree with the noun in gender and number.

Since materiale is masculine singular, the adjective must also be masculine singular:

• puro = masculine singular
• pura = feminine singular
• puri = masculine plural
• pure = feminine plural

Examples:

• Questo materiale è puro.
• Questa sostanza è pura.
• Questi materiali sono puri.
• Queste sostanze sono pure.

In Italian, descriptive adjectives often come after the noun, especially in straightforward factual statements.

So materiale puro is the normal order for pure material.

In the full sentence:

• Questo materiale è puro = This material is pure

That structure is:

• Questo materiale = subject
• è = verb
• puro = adjective describing the subject

Italian can sometimes place adjectives before the noun, but after the noun is very common and often the most neutral choice.

Yes, but it means something slightly different in structure.

• Questo materiale è puro = This material is pure.
• Questo è un materiale puro = This is a pure material.

The first sentence talks directly about the material. The second first says this is and then identifies it as a pure material.

So both are possible, but they are not exactly the same sentence pattern.

It can work either way depending on context.

In Questo materiale è puro, materiale is being used in a general sense, similar to English material.

But Italian materiale can also be countable:

• un materiale = a material
• i materiali = materials

So the word itself can be either countable or more general, depending on how it is used.

A simple pronunciation guide is:

KWEH-stoh mah-teh-ree-AH-leh eh POO-roh

A few notes:

• questo: the beginning sounds roughly like kweh
• materiale: the stress is on -a- in -ria-
• è: pronounced like eh
• puro: stress on pu-

If you want it more syllable by syllable:

• ques-to
• ma-te-ria-le
• è
• pu-ro

Yes, that is possible, but it changes the emphasis.

• Questo materiale è puro = neutral, standard statement
• È puro questo materiale = more marked, often emphasizing puro or sounding contrastive

For a learner, the normal version to use is:

Questo materiale è puro.

The plural would be:

Questi materiali sono puri.

Here is what changes:

• questo → questi
• materiale → materiali
• è → sono
• puro → puri

So everything agrees in number as well as gender.

Yes. In many cases it directly matches English pure, especially for substances or materials.

For example, it can mean:

• chemically pure
• unmixed
• not contaminated

But like English pure, it can also have wider uses in other contexts, such as moral or figurative meanings. In this sentence, because the noun is materiale, the most natural interpretation is the physical one: the material is pure or unmixed.