Возврат возможен в течение недели, а обмен — в течение месяца.

Because it agrees with возврат, which is a masculine singular noun.

• возврат = masculine singular
• возможен = short-form adjective, masculine singular

In Russian, short-form adjectives often act like is possible / is allowed / is available in English. So Возврат возможен literally works like Return is possible.

If the noun were feminine, you would get возможна.
If it were plural, возможны.

Возможен is the short form of the adjective возможный.

Russian often uses short-form adjectives in statements like this, especially in formal notices, rules, and business language.

• возможный = full form, more like possible as a regular describing adjective
• возможен = short form, often used predicatively, like is possible

So:

• Возврат возможен = Return is possible
• not usually Возврат возможный in this context

The short form is the normal choice here.

The dash shows that something is omitted in the second part because it is understood from the first part.

Full version:

• Возврат возможен в течение недели, а обмен возможен в течение месяца.

But Russian often avoids repeating the same words, especially in neat, written statements. So the second возможен is left out:

• Возврат возможен в течение недели, а обмен — в течение месяца.

The dash marks that gap. In English, we might do something similar with return is possible within a week, and exchange — within a month, though English usually prefers to repeat the verb less dramatically.

А often connects two things by contrasting or comparing them, even when both statements are true.

Here the sentence compares two policies:

• return: one week
• exchange: one month

So а is very natural because it means something like:

• whereas
• while
• but as for

Using и would simply add information: and.
Using а highlights the difference between the two time limits.

After в течение, Russian uses the genitive case.

So:

• неделя → недели
• месяц → месяца

This is a fixed prepositional expression:

• в течение + genitive

It means during, within the period of, or in the course of depending on context.

Examples:

• в течение дня = during the day
• в течение года = during the year
• в течение недели = within/during a week

In this sentence, it means the action is allowed within that time period.

No, they are different.

• в течение недели = within a week / during the period of a week
• через неделю = in a week / one week later

So:

• Возврат возможен в течение недели = you have the right to return it anytime during that week
• Возврат возможен через неделю would mean the return is possible one week later, which is a different idea

That is why в течение is the correct expression here.

Because в течение requires the genitive case.

The dictionary form is:

• месяц

But after в течение, it changes to:

• месяца

So:

• в течение месяца
• not в течение месяц

This is just normal case grammar.

Yes. Возврат and обмен are nouns, and they sound more formal, compact, and typical of store policies, signs, and legal/business language.

Compare:

• Возврат возможен в течение недели.
• Товар можно вернуть в течение недели.

Both are correct, but the second is more direct and conversational: You can return the item within a week.

Likewise:

• Обмен возможен...
• Товар можно обменять...

Using nouns like возврат and обмен gives the sentence a formal, policy-style tone.

Yes, very possibly. In real-life contexts, Russian often leaves out obvious words.

For example, the fuller idea might be:

• Возврат товара возможен...
• Обмен товара возможен...

But if the context is already clear, Russian often shortens this to just:

• Возврат возможен...
• Обмен...

This is especially common on signs, receipts, store websites, and policy notices.

Yes, but the original order is natural and standard for a formal notice.

Original:

• Возврат возможен в течение недели, а обмен — в течение месяца.

Possible variations:

• В течение недели возможен возврат, а в течение месяца — обмен.

That version is also correct, but it sounds more structured or emphatic. The original is smoother and more typical in policy language.

Russian word order is flexible, but not random. Different orders change the focus slightly.

Russian has no articles like a, an, or the.

So where English says:

• within a week
• within the month
• during the week

Russian simply uses the noun with the correct case:

• в течение недели
• в течение месяца

The exact English article depends on context, but Russian does not mark that distinction here.

Yes, it sounds fairly formal and typical of administrative or commercial Russian.

Clues:

• the use of nouns возврат and обмен
• the short-form adjective возможен
• the compressed second clause with a dash
• the expression в течение

This is the kind of Russian you might see in:

• store policies
• official notices
• product pages
• receipts
• legal or customer-service text

In everyday conversation, people might say something more like:

• Вернуть можно в течение недели, а обменять — в течение месяца.

That is less formal but means the same thing.

It has two coordinated parts:

1. Возврат возможен в течение недели
2. а обмен — в течение месяца

The second part is shortened. The omitted word is возможен.

So the full grammatical pattern is:

• [noun] + [short-form adjective] + [time expression]
• [noun] + [same omitted adjective] + [time expression]

This kind of parallel structure is very common in Russian formal writing because it is concise and elegant.