Giáo viên sẽ giải thích lại nếu bài tập này rất khó.

Yes—sẽ usually marks a future action or a prediction, so here it shows that the teacher will explain again.

A few useful points:

• sẽ often corresponds to English will
• It goes before the verb
• In this sentence, it comes before giải thích

So:

• Giáo viên sẽ giải thích lại = The teacher will explain again

Also, Vietnamese does not always have to mark the future. In many everyday sentences, speakers can leave out sẽ if the time is already clear from context. But using sẽ makes the future meaning more explicit.

Here, lại means again, so giải thích lại means explain again or re-explain.

In Vietnamese, words like lại often come after the verb, not before it as in English.

So:

• giải thích = explain
• giải thích lại = explain again

This word order is very natural in Vietnamese. English says again after the whole verb phrase or before it sometimes, but Vietnamese commonly places lại directly after the verb.

Because Vietnamese demonstratives usually come after the noun.

So:

• bài tập này = this exercise
• literally: exercise this

This is a very common Vietnamese pattern:

• nhà này = this house
• người đó = that person
• cuốn sách này = this book

So even though English says this exercise, Vietnamese says exercise this.

Nếu means if. It introduces a condition.

In your sentence:

• nếu bài tập này rất khó = if this exercise is very difficult

So the whole sentence has the pattern:

• main clause + nếu + condition
• Giáo viên sẽ giải thích lại nếu bài tập này rất khó.

Vietnamese can also put the if-clause first, just like English:

• Nếu bài tập này rất khó, giáo viên sẽ giải thích lại.

Both are correct. The meaning stays the same.

Because Vietnamese often does not need a verb like to be before adjectives.

In English, we say:

• This exercise is very difficult

But in Vietnamese, adjectives can function directly as predicates:

• bài tập này rất khó
• literally: this exercise very difficult

So there is no separate word for is here. That is normal Vietnamese grammar.

Rất means very.

It goes before the adjective:

• rất khó = very difficult

This is the normal position in Vietnamese:

• rất tốt = very good
• rất nhanh = very fast
• rất đẹp = very beautiful

So in this sentence:

• bài tập này rất khó = this exercise is very difficult

Vietnamese does not have articles like a, an, and the in the same way English does.

So giáo viên can mean:

• a teacher
• the teacher
• teachers in some contexts

The exact meaning depends on context.

In this sentence, the intended meaning is clearly the teacher or the teacher(s) in context, even though there is no separate word for the.

This is very normal in Vietnamese. Context does a lot of the work that articles do in English.

Bài tập means exercise, assignment, or sometimes homework exercise, depending on context.

About bài:

• bài can function as part of a compound noun here
• In bài tập, the whole expression is learned as a set phrase meaning exercise

So it is best to treat bài tập as one vocabulary item.

You may also see bài used with things like:

• bài hát = song
• bài viết = piece of writing/article
• bài học = lesson

So while bài has its own meaning in some contexts, for learners it is most helpful here to memorize bài tập as exercise.

Yes.

• bài tập này khó = this exercise is difficult
• bài tập này rất khó = this exercise is very difficult

Adding rất makes the difficulty stronger.

So the original sentence suggests that the teacher will explain again if the exercise is very difficult, not just a little difficult.

Yes, in some contexts it could be omitted:

• Giáo viên giải thích lại nếu bài tập này rất khó.

This can still be understood as something the teacher does or will do, depending on context.

However, with sẽ, the sentence more clearly means:

• The teacher will explain again if this exercise is very difficult.

So sẽ is helpful when you want to clearly mark future or intended action.

Mostly yes, but with a few important differences.

The sentence breaks down like this:

• Giáo viên = teacher
• sẽ = will
• giải thích lại = explain again
• nếu = if
• bài tập này = this exercise
• rất khó = very difficult

So the order is fairly similar to English:

• Teacher + will + explain again + if + this exercise + very difficult

The main differences are:

• này comes after the noun
• there is no word for is
• lại comes after the verb
• there are no articles like the

So it is similar overall, but not identical.

Yes, absolutely.

That version puts the condition first:

• Nếu bài tập này rất khó, giáo viên sẽ giải thích lại.
• If this exercise is very difficult, the teacher will explain again.

This is completely natural Vietnamese.

So both of these are correct:

• Giáo viên sẽ giải thích lại nếu bài tập này rất khó.
• Nếu bài tập này rất khó, giáo viên sẽ giải thích lại.

The difference is mostly about emphasis and flow, not basic meaning.