Банан — один из самых удобных фруктов для быстрого завтрака.

In Russian, a dash is often used in sentences where English would use is.

So:

• Банан — один из самых удобных фруктов...
• literally: A banana — one of the most convenient fruits...

Russian usually omits the verb to be in the present tense, and the dash helps show the link between the subject and the rest of the sentence.

You could think of the dash here as standing in for is.

Russian often uses the singular to talk about something in a general, classifying way.

So Банан here means something like:

• The banana
• A banana
• Bananas as a type of fruit

English can do this too, though not always in exactly the same way. Compare:

• The banana is a very practical fruit.
• A banana is one of the most convenient fruits.

So the singular is natural here because the sentence is making a general statement about bananas as a kind of food.

Один из means one of.

This is a very common Russian pattern:

• один из лучших фильмов = one of the best films
• одна из причин = one of the reasons
• одно из решений = one of the solutions

After один из, Russian normally uses the genitive plural for the group being referred to.

So:

• один из фруктов = one of the fruits
• один из самых удобных фруктов = one of the most convenient fruits

Because after один из, the noun that names the group goes in the genitive plural.

Here the base noun is:

• фрукт = fruit

Its genitive plural is:

• фруктов

So:

• один из фруктов = one of the fruits

This is just a standard grammar pattern in Russian.

Because самых удобных фруктов is part of the один из structure.

After один из, the whole phrase describing the group must be in the genitive plural:

• один из самых удобных фруктов

That means:

• фруктов is genitive plural
• удобных agrees with фруктов
• самых also matches that form

If you said самые удобные фрукты, that would be nominative plural, which would not fit after один из.

Compare:

• Это самые удобные фрукты. = These are the most convenient fruits.
• Банан — один из самых удобных фруктов. = A banana is one of the most convenient fruits.

The superlative here is made with:

• самый
  • adjective

So:

• удобный = convenient
• самый удобный = the most convenient

But because the phrase must agree with фруктов in the genitive plural, it becomes:

• самых удобных

This is just agreement:

• masculine singular nominative: самый удобный
• plural genitive: самых удобных

So the sentence uses the normal, very common Russian way of saying most convenient.

Not exactly. Удобный often means convenient, practical, or easy to use/handle.

It can sometimes mean comfortable, but that depends on context.

Here, with food, удобный means something like:

• easy to eat
• practical
• not messy
• easy to take with you
• good for a quick meal

So in this sentence, удобных фруктов means convenient/practical fruits, not comfortable fruits.

Для usually means for.

So:

• для быстрого завтрака = for a quick breakfast

It shows purpose or suitability.

The sentence is saying that a banana is one of the most convenient fruits for that purpose.

Other examples:

• чашка для кофе = a cup for coffee
• место для отдыха = a place for rest
• время для работы = time for work

Because для requires the genitive case.

The dictionary form is:

• завтрак = breakfast

After для, it becomes:

• для завтрака

And since the adjective must agree with it:

• для быстрого завтрака

So this is not specific to this sentence; it is a general rule:

• для
  • genitive

Because after для, both the noun and its adjective must go into the genitive.

Base forms:

• быстрый завтрак = a quick breakfast
  nominative

After для:

• для быстрого завтрака = for a quick breakfast
  genitive

The adjective changes from быстрый to быстрого to agree with завтрака.

Yes, literally it means a quick breakfast.

In practice, that usually means:

• a breakfast that is quick to prepare
• quick to eat
• convenient when you do not have much time

So the phrase is natural, even though literally breakfast is being described as quick.

English does the same thing in phrases like a quick lunch or a quick snack.

Yes, Russian word order is fairly flexible.

The original sentence is natural and neutral:

• Банан — один из самых удобных фруктов для быстрого завтрака.

But you could also say, for example:

• Для быстрого завтрака банан — один из самых удобных фруктов.

That version puts more emphasis on for a quick breakfast.

Russian word order often changes the emphasis rather than the basic meaning.

Yes, it could.

For example:

• Банан — это один из самых удобных фруктов для быстрого завтрака.

This sounds a little more explanatory or emphatic, as if defining or clarifying something.

Without это, the sentence is simpler and very natural.
With это, it can sound slightly more like:

• A banana is, in fact, one of the most convenient fruits...

Both are possible.

They agree with фруктов, which is genitive plural.

So all the describing words must also be genitive plural:

• самый → самых
• удобный → удобных
• фрукт → фруктов

This is a very important Russian habit: adjectives and similar words match the noun in gender, number, and case.

So once you know that один из requires genitive plural, the rest follows by agreement.

If you wanted to speak about bananas in general in the plural, you might say:

• Бананы — одни из самых удобных фруктов для быстрого завтрака.

Notice the changes:

• Банан → Бананы
• один → одни

That means:

• Bananas are among the most convenient fruits for a quick breakfast.

So the original singular and a plural version are both possible, but the singular is a nice general statement about the banana as a type of fruit.