Контактные линзы требуют раствора для линз.

Because it has to agree with линзы.

• линза = lens
• контактный = contact (adjective)

Here the noun is plural and is the subject, so it is in the nominative plural: линзы. The adjective matches it, so контактный becomes контактные.

So:

• контактная линза = a contact lens
• контактные линзы = contact lenses

Because the sentence is talking about contact lenses in general, not one specific lens.

• контактная линза = one contact lens
• контактные линзы = contact lenses

Russian often uses the plural when speaking about something as a category or a typical pair/set. If you used the singular here, it would sound like you were talking about one individual lens.

Because the subject is plural: контактные линзы.

Russian verbs in the present tense agree with the subject in number:

• линза требует = the lens requires
• линзы требуют = the lenses require

So требуют is the 3rd person plural form of требовать.

Раствора is the genitive singular form of раствор.

With требовать, Russian often uses the genitive for the thing that is required, especially with things like substances, materials, or something needed in a general sense:

• требовать внимания = to require attention
• требовать помощи = to require help
• требовать раствора = to require solution

So here:

• раствор = dictionary form
• раствора = genitive singular

A useful way to feel it is: require some amount of solution.

It is genitive plural.

The preposition для means for, and it normally requires the genitive case:

• для линзы = for a lens
• для линз = for lenses

So:

• раствор для линз = solution for lenses

This is a very common Russian pattern: noun + для + genitive.

It is a little repetitive by English standards, but it is completely normal in Russian.

The first линзы is the subject: contact lenses.
The second линз is part of the phrase раствор для линз = lens solution / solution for lenses.

Russian is often less worried than English about repeating a noun if it keeps the sentence clear and natural.

You could replace the second part with something like для них = for them, but that would usually sound less natural here.

It can mean all of those, depending on the subject and context.

With a person, it can mean demand:

• Он требует ответа. = He demands an answer.

With an inanimate thing, it usually means require / need:

• Машина требует ремонта. = The car needs repairs.
• Контактные линзы требуют раствора. = Contact lenses require solution.

So in this sentence, it does not sound like the lenses are literally making demands. It simply means they need it.

Yes, absolutely.

In fact, раствор для контактных линз is very common and more explicit:

• раствор для линз = solution for lenses
• раствор для контактных линз = solution for contact lenses

The shorter version works because the context already mentions contact lenses, so Russian can leave контактных out the second time.

It is correct and natural, especially in a neutral or slightly formal style.

But in everyday Russian, people might also say:

• Для контактных линз нужен раствор.
• Контактным линзам нужен раствор.

These sound a bit more like ordinary spoken Russian: Contact lenses need solution.

The original sentence is still perfectly fine, especially in informational or textbook-style language.

Because Russian has no articles.

So Russian nouns usually appear without words equivalent to a, an, or the. Context tells you whether the meaning is definite or indefinite.

That means раствора here could be understood in English as:

• solution
• a solution
• the solution

depending on context. In natural English, though, we usually say lens solution or solution for contact lenses.

A close literal breakdown is:

• Контактные линзы = contact lenses
• требуют = require
• раствора = solution (genitive: of solution / some solution)
• для линз = for lenses

So very literally, it is something like:

Contact lenses require solution for lenses.

That sounds a bit awkward in English, but the Russian structure is normal.

The stress is:

конта́ктные ли́нзы тре́буют раство́ра для линз

A rough pronunciation guide:

• конта́ктные ≈ kon-TAKT-ny-ye
• ли́нзы ≈ LEEN-zï
• тре́буют ≈ TRE-bu-yut
• раство́ра ≈ ras-TVOR-a
• для ≈ dlya
• линз ≈ leenz

The biggest thing to remember is the stress positions, especially in тре́буют and раство́ра.