Этот кочан капусты тяжёлый, зато редис очень свежий.

Because the main noun here is кочан, not капуста.

In этот кочан капусты, the structure is:

• кочан = head
• капусты = of cabbage

So the whole phrase means this head of cabbage. Since кочан is masculine, the demonstrative has to be masculine too: этот.

That is also why the adjective later is тяжёлый and not тяжёлая.

Because Russian often uses the genitive after a noun that names a container, unit, or piece of something.

So:

• кочан = a head
• капусты = of cabbage

This is very similar to English a head of cabbage, a cup of tea, a piece of bread.

Other examples:

• чашка чая = a cup of tea
• кусок хлеба = a piece of bread
• бутылка воды = a bottle of water

So кочан капусты is a normal pattern.

Кочан means a head of a leafy vegetable, especially cabbage.

So кочан капусты is specifically a head of cabbage, not just cabbage in general.

If you said эта капуста, that would mean this cabbage more generally.
If you say этот кочан капусты, you are talking about one physical cabbage head as a single item.

Because тяжёлый agrees with кочан, which is masculine singular nominative.

Agreement in Russian affects adjectives and similar words. Here:

• кочан = masculine singular
• so этот = masculine singular
• and тяжёлый = masculine singular

If the noun were feminine, you would get forms like:

• эта сумка тяжёлая = this bag is heavy

But here the noun being described is кочан, so masculine forms are required.

In Russian, the verb to be is normally omitted in the present tense.

So:

• Этот кочан капусты тяжёлый literally looks like This head of cabbage heavy
• but it means This head of cabbage is heavy

This is completely normal Russian.

Compare:

• Он дома = He is at home
• Она врач = She is a doctor
• Редис свежий = The radish is fresh / Radishes are fresh

In the past and future, forms of to be do appear:

• был, была, было, были
• будет, будут, etc.

Not exactly.

Зато introduces a contrast, but usually with the idea of compensation: one thing is bad or less ideal, but on the plus side something else is good.

So here:

• Этот кочан капусты тяжёлый = This head of cabbage is heavy
• зато редис очень свежий = but/on the other hand the radishes are very fresh

A natural feeling of зато is:

• but at least
• but on the other hand
• but the good thing is

By contrast, но is a more neutral but.

Example:

• Квартира маленькая, но уютная = The apartment is small but cozy
• Дорого, зато качественно = It’s expensive, but at least it’s good quality

So зато is a very good choice if the second part partly makes up for the first.

Because зато is a coordinating conjunction joining two clauses, and Russian normally puts a comma before it.

So:

• Этот кочан капусты тяжёлый, зато редис очень свежий.

This is standard punctuation, just like a comma before but in many English sentences.

Yes. In Russian, редис is grammatically singular masculine, but it can be used collectively to mean radish/radishes as a product or vegetable.

So редис очень свежий is a natural market-style way to say that the radishes are very fresh.

If you want to talk about separate individual radishes, you can use the plural редиски.

Compare:

• Редис очень свежий = The radish is very fresh / The radishes are very fresh
• Эти редиски маленькие = These radishes are small

So the singular here does not necessarily mean exactly one radish.

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

• редис = masculine singular
• therefore свежий = masculine singular

If the noun were plural, you would use:

• свежие

For example:

• Редиски очень свежие = The radishes are very fresh

So the form of the adjective tells you how the speaker is treating the noun grammatically.

Yes, you could, but it would not mean exactly the same thing.

• Эта капуста тяжёлая = This cabbage is heavy
• Этот кочан капусты тяжёлый = This head of cabbage is heavy

The second version is more specific and sounds like you are talking about one actual cabbage head, perhaps at a market or in a kitchen.

So both are grammatical, but кочан капусты is more concrete and precise.

The word order is fairly neutral.

• Этот кочан капусты тяжёлый is a normal way to say This head of cabbage is heavy
• зато редис очень свежий is also natural and neutral

Russian word order is more flexible than English, but changing it usually changes emphasis rather than basic meaning.

For example, you might move words around for contrast or focus, but the version you were given sounds like an ordinary descriptive statement.

Очень means very.

It usually goes right before the adjective or adverb it modifies:

• очень свежий = very fresh
• очень тяжёлый = very heavy
• очень быстро = very quickly

So редис очень свежий simply means the radish/radishes are very fresh. The placement is exactly what you would expect in standard Russian.