Авокадо оказалось мягким, а манго — очень сладким.

Because the subject is авокадо, and in Russian авокадо is normally treated as an indeclinable neuter singular noun.

In the past tense, Russian verbs agree with the subject in gender and number:

• он оказался — masculine
• она оказалась — feminine
• оно оказалось — neuter
• они оказались — plural

So:

• авокадо оказалось
• манго оказалось

Both авокадо and манго are usually treated as оно words in standard Russian.

Оказаться means something like to turn out to be or to prove to be.

So оказалось мягким is not just a neutral description. It suggests a result or discovery:

• you cut the avocado open
• checked it
• and it turned out to be soft

If you say было мягким, that simply means was soft.
If you say оказалось мягким, it adds the idea of finding out.

So the difference is roughly:

• Авокадо было мягким — The avocado was soft
• Авокадо оказалось мягким — The avocado turned out to be soft

After verbs like быть, стать, оказаться, Russian often uses the instrumental case for the predicate adjective or noun.

So:

• оказалось мягким
• оказалось сладким

This is the normal pattern after оказаться.

A useful way to think about it is:

• авокадо оказалось мягким = the avocado turned out to be soft
• манго оказалось сладким = the mango turned out to be sweet

The instrumental ending here is:

• мягкий → мягким
• сладкий → сладким

Because both adjectives agree with neuter singular nouns used in this predicate structure.

The dash shows that a word has been left out because it is understood from the first clause.

The full version would be:

• Авокадо оказалось мягким, а манго оказалось очень сладким.

In the actual sentence, the second оказалось is omitted to avoid repetition:

• Авокадо оказалось мягким, а манго — очень сладким.

This is very common in Russian writing, especially when two parts are parallel.

So the dash here basically means:

• манго — [оказалось] очень сладким

А often links two things by comparison or contrast.

Here it works like:

• whereas
• while
• sometimes and
• sometimes but, depending on context

In this sentence, а sets the two fruits against each other:

• the avocado turned out soft,
• whereas the mango was very sweet

It is not a strong contradiction. It is more of a contrastive pairing.

Compare:

• и — simple addition
• но — stronger contrast, more like but
• а — contrast, comparison, switching from one topic/item to another

Usually no. Both are commonly treated as indeclinable loanwords, which means their form stays the same.

So you typically get the same form in different roles:

• авокадо
• манго

What changes instead is:

• the surrounding words
• adjective agreement
• verb agreement
• prepositions
• word order

For example:

• Это спелое авокадо
• Я купил авокадо
• Мы говорили об авокадо

The noun itself stays the same.

It could repeat it, and that would still be grammatical:

• Авокадо оказалось мягким, а манго оказалось очень сладким.

Russian often drops repeated words when the meaning is obvious.
That makes the sentence sound lighter and more natural.

So both are possible:

• full version with repetition
• shorter version with a dash

The shorter version is especially common in written Russian when the structure is parallel.

Because очень normally goes before the adjective it modifies:

• очень сладкий
• очень мягкий
• очень вкусный

So in this sentence:

• очень сладким = very sweet

This is the most neutral and natural order.

Other orders are possible only with special emphasis or in unusual contexts, but for a learner, the standard pattern is:

• очень + adjective

Yes. Russian word order is flexible, and you could reverse the two parts if the context supports it:

• Манго оказалось очень сладким, а авокадо — мягким.

The choice depends on what the speaker wants to mention first or emphasize first.

In the original sentence, авокадо comes first simply because that is the first item being discussed. The sentence then contrasts it with манго.

Yes, but that is a different structure.

• Авокадо мягкое, а манго очень сладкое — The avocado is soft, and the mango is very sweet
• Авокадо оказалось мягким, а манго — очень сладким — The avocado turned out to be soft, and the mango turned out to be very sweet

The first version is a plain statement.
The second version adds the idea of discovery or result.

So the original sentence is not just describing the fruit. It suggests that after checking or tasting them, that is what they turned out to be.