Para el intercambio de ropa, clasificamos cada retal.

Para here expresses purpose or intended use: for the clothing exchange.

So Para el intercambio de ropa means something like:

• For the clothing exchange
• For the clothes swap
• For use in the clothing exchange

A very common pattern in Spanish is:

• para + noun
• para + infinitive

Examples:

• Para la fiesta, compramos comida. — For the party, we bought food.
• Para coser, necesito hilo. — To sew, I need thread.

In your sentence, para gives the context in which the action is done.

Spanish often uses the definite article el / la / los / las more often than English does.

Here, el intercambio de ropa refers to a specific event or activity:

• the clothing exchange
• the clothes swap

Even if English might sometimes say simply for a clothing exchange or for clothing exchange, Spanish often prefers the article when talking about a known or understood thing.

Compare:

• Voy al mercado. — I’m going to the market.
• Preparamos todo para la reunión. — We prepare everything for the meeting.

So el is very natural here.

Spanish frequently uses de + noun where English might use another noun as an adjective.

So:

• intercambio de ropa = exchange of clothes = clothing exchange
• tienda de ropa = clothes shop
• lavadora de ropa = clothes washing machine / washing machine for clothes

English often stacks nouns together:

• clothing exchange
• car door
• coffee cup

Spanish usually prefers:

• intercambio de ropa
• puerta del coche
• taza de café

So de ropa is the normal Spanish way to specify what kind of exchange it is.

Clasificamos is the first person plural form of clasificar in the present tense:

• yo clasifico — I classify
• tú clasificas — you classify
• él/ella clasifica — he/she classifies
• nosotros/nosotras clasificamos — we classify
• vosotros/vosotras clasificáis — you all classify
• ellos/ellas clasifican — they classify

So clasificamos means we classify or we are classifying, depending on context.

Spanish usually does not need the subject pronoun because the verb ending already shows who is doing the action. That is why nosotros is omitted.

• Clasificamos cada retal. = We classify each scrap/remnant.
• Nosotros clasificamos cada retal. = same meaning, but with extra emphasis on we

So the sentence sounds more natural without nosotros unless you want contrast or emphasis.

By itself, clasificamos can mean either:

• we classify / we are classifying — present
• we classified — preterite

This happens because some -ar verbs have the same spelling for:

• present nosotros
• preterite nosotros

For example:

• hablamos
• trabajamos
• clasificamos

So how do you know which one it is? Context.

In this sentence, Para el intercambio de ropa, clasificamos cada retal, the most natural reading is usually present:

• For the clothing exchange, we classify each scrap

But in the right context, it could also be past:

• For the clothing exchange, we classified each scrap

If the broader context is telling a story about completed actions, the past reading is possible.

Retal is a noun that usually refers to a piece of leftover cloth, a fabric remnant, or a scrap of cloth.

It is not one of the most basic everyday words for beginners, so it may stand out.

In Spain, retal is commonly associated with sewing, fabric, textiles, and leftover material from cutting.

Roughly:

• retal = remnant
• retal de tela = scrap/remnant of fabric

So cada retal means:

• each fabric scrap
• each remnant
• each leftover piece of cloth

If the meaning shown to the learner says something broader, it is still useful to know that retal has this textile-specific sense.

Both are possible, but they are used a little differently.

cada retal

Focuses on items one by one:

• each scrap
• we classify them individually

todos los retales

Focuses on the whole set:

• all the scraps

Compare:

• Clasificamos cada retal. — We classify each scrap.
• Clasificamos todos los retales. — We classify all the scraps.

Also, after cada, Spanish normally uses the singular:

• cada retal
• cada prenda
• cada caja

Not:

• cada retales

So the singular after cada is completely normal.

The personal a is usually used before a specific person or sometimes a personified being as a direct object.

Examples:

• Veo a María.
• Conocemos a tu hermano.

But retal is a thing, not a person, so there is no personal a:

• Clasificamos cada retal.

That is exactly what you would expect.

The comma is possible because Para el intercambio de ropa is an introductory phrase.

Spanish often allows a comma after a fronted introductory element, especially when the phrase is a little longer:

• Para la fiesta, compramos bebidas.
• Después de cenar, salimos a pasear.

Without the comma, the sentence is still understandable:

• Para el intercambio de ropa clasificamos cada retal.

But the comma helps separate the introductory purpose phrase from the main clause. It makes the sentence easier to read.

So:

• with comma = clear and very natural
• without comma = also possible, especially in less formal writing

It is grammatically correct, but whether it sounds fully natural depends on the intended meaning.

The part that may feel unusual is retal, because it specifically suggests fabric remnants. If the sentence is really about sorting leftover pieces of cloth for a clothing-related exchange, it works.

But if the idea is sorting actual clothes, a native speaker might more naturally say:

• Para el intercambio de ropa, clasificamos cada prenda. — each garment
• Para el intercambio de ropa, clasificamos la ropa por categorías. — we sort the clothes by category
• Para el intercambio de ropa, separamos cada pieza. — we separate each item

So the sentence is fine if retal is truly the right noun for the objects involved. If the meaning shown to the learner is about clothes in general, retal may be more specialized than expected.

Yes. In Spanish, intercambio de ropa can refer to a clothing exchange or clothes swap, where people bring clothes and exchange them.

Depending on context, a native speaker might also say:

• trueque de ropa
• mercadillo de intercambio de ropa
• intercambio de prendas

But intercambio de ropa is clear and understandable.

So if the context is an event where clothes are exchanged, that phrase works well.