Questo è un buon affare.

Questo means this and is a masculine singular demonstrative. It points to something near the speaker, just like English this.

In Questo è un buon affare, questo is standing on its own as a pronoun: This is...

If the noun were stated explicitly, you might also see:

• Questo affare è buono = This deal is good

But in your sentence, the noun is not repeated after questo, because questo already means this (thing / this one).

Because questo is the masculine singular form.

Italian demonstratives must match the gender and number of the noun they refer to:

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

Since affare is a masculine singular noun, questo fits.

For example:

• Questo è un buon affare = masculine singular
• Questa è una buona idea = feminine singular

The accent distinguishes è = is from e = and.

So:

• è = third person singular of essere = is
• e = and

This accent is very important in writing:

• Questo è buono = This is good
• pane e formaggio = bread and cheese

Italian uses different forms of the indefinite article depending on the sound that follows.

For masculine singular nouns:

• un before most consonants and vowels
• uno before s + consonant, z, ps, gn, and similar sounds

Since affare begins with a vowel, Italian uses un:

• un affare
• un amico

But:

• uno studente
• uno zaino

This is a very common pattern. Buono becomes buon before most masculine singular nouns.

So:

• buono = dictionary form
• buon affare = good deal
• buon libro = good book

This shortening happens when buono comes before a masculine singular noun, much like:

• bello can become bel

But note:

• buono studente is not correct
• it becomes buono studente? Actually, with nouns that take uno, the adjective usually stays fuller: un buono studente is possible, though in real usage Italians often prefer other phrasing depending on meaning

For your sentence, buon affare is the normal and natural form.

In Italian, adjectives can come before or after the noun, but the position can affect style or nuance.

With very common descriptive adjectives like buono, putting the adjective before the noun is extremely normal:

• un buon affare
• un bel giorno
• una brava persona

If you say un affare buono, it sounds unnatural here. In most everyday situations, Italians would say un buon affare.

So this is not just grammar; it is also natural usage.

In this sentence, affare means deal, bargain, or good buy.

It can also have other meanings depending on context, such as:

• business matter
• affair
• belonging / thing in some contexts

But in Questo è un buon affare, the most natural meaning is:

• This is a good deal
• This is a bargain

So affare is one of those nouns whose meaning depends a lot on context.

The plural is affari.

So:

• un affare = a deal
• due affari = two deals

And the full sentence in the plural could be:

• Questi sono buoni affari = These are good deals

Notice how everything changes to match:

• questi instead of questo
• sono instead of è
• buoni affari instead of buon affare

A simple approximate pronunciation for an English speaker is:

KWEH-stoh eh oon bwon ah-FAH-reh

A few helpful points:

• qu in questo sounds like kw
• è is a clear open eh
• buon sounds roughly like bwon
• affare has stress on -fa-: af-FA-re

If you want to sound more natural, keep the vowels clear and short rather than reducing them as much as in English.

Grammatically, Italian sometimes allows adjective placement after the noun, but in this case un buon affare is the standard natural expression.

Un affare buono sounds awkward and not like the usual way to express a good deal.

So for a learner, the safe choice is:

• un buon affare

Think of it as a set phrase you should memorize.

Just add non before the verb:

• Questo non è un buon affare = This is not a good deal

This is the normal way to form a basic negative sentence in Italian:

• non + verb

Examples:

• Questo è interessante = This is interesting
• Questo non è interessante = This is not interesting

In Italian, you can often make a question just by using your voice and raising intonation at the end:

• Questo è un buon affare? = Is this a good deal?

The word order usually stays the same. Italian does not usually require inversion like English does.

You could also ask more naturally in conversation:

• È un buon affare, questo?
• Questo è davvero un buon affare? = Is this really a good deal?

It is neutral. It works in both everyday and fairly formal situations.

You could say it:

• while shopping
• when discussing a contract
• when commenting on a price
• in casual conversation

Nothing in Questo è un buon affare is especially formal, slangy, or literary. It is standard Italian.