Vấn đề này khó giải.

In Vietnamese, demonstratives like này (this) usually come after the noun.

So:

• vấn đề này = this problem / this issue
• not này vấn đề

This is very normal Vietnamese word order. English says this problem, but Vietnamese says problem this.

A few similar examples:

• cuốn sách này = this book
• người này = this person

Vietnamese often does not use a copula like is before adjectives.

So:

• Vấn đề này khó. = This problem is difficult.

Here, khó (difficult) can directly be the predicate of the sentence.

Using là here would usually sound unnatural. Vietnamese normally says:

• Vấn đề này khó giải.

not:

• Vấn đề này là khó giải.

So the lack of is is completely normal.

Vietnamese does not have an infinitive marker like English to in this kind of structure.

So:

• khó giải = hard to solve
• literally something like difficult solve

This pattern is very common:

• dễ hiểu = easy to understand
• khó tin = hard to believe
• dễ làm = easy to do

So khó giải is a standard Vietnamese pattern: adjective + verb.

khó giải is an adjective-like expression meaning difficult to solve.

Breakdown:

• khó = difficult, hard
• giải = solve

Together they describe the noun phrase vấn đề này.

So the whole sentence works like this:

• Vấn đề này = this problem
• khó giải = is hard to solve

This is a very common Vietnamese structure where an adjective is followed by a verb to show what is difficult, easy, convenient, dangerous, etc.

That is a very good question.

Yes, giải can mean solve, but with vấn đề many learners will also see giải quyết, which is often more explicit and common in everyday Vietnamese.

Compare:

• Vấn đề này khó giải.
• Vấn đề này khó giải quyết.

Both can mean This problem is difficult to solve.

Nuance:

• giải is shorter and more compact
• giải quyết is more explicit: resolve / deal with / solve

With vấn đề, khó giải quyết may sound a bit more natural in ordinary speech, while khó giải can sound concise, formal, or slightly literary depending on context.

Yes, it is natural, but it is somewhat compact.

In everyday speech, many speakers might also say:

• Vấn đề này khó giải quyết.
• Vấn đề này không dễ giải quyết.

So Vấn đề này khó giải is correct and natural, but it may feel a little more concise than the most conversational version.

Yes. Vấn đề này khó is grammatical and natural.

The difference is:

• Vấn đề này khó = This problem is difficult.
• Vấn đề này khó giải = This problem is difficult to solve.

So when you add giải, you make the meaning more specific. Without giải, khó is broader and could mean the problem is difficult in general.

Yes, but the meaning changes a little.

• vấn đề = problem, issue, question, matter
• bài toán = math problem, or sometimes a figurative problem/challenge

So:

• Bài toán này khó giải. often sounds very natural for a literal math problem.
• Vấn đề này khó giải. is better for a general issue or problem.

If the sentence is about a social, political, or practical issue, vấn đề is usually the better choice.

You can add degree words very easily.

Examples:

• Vấn đề này rất khó giải. = This problem is very hard to solve.
• Vấn đề này khá khó giải. = This problem is fairly hard to solve.
• Vấn đề này không khó giải. = This problem is not hard to solve.
• Vấn đề này không dễ giải. = This problem is not easy to solve.

These are all natural extensions of the same pattern.

The neutral, standard order is:

• Vấn đề này khó giải.

You can change it for emphasis, but that changes the tone.

For example:

• Vấn đề này thì khó giải.

The thì marks vấn đề này as the topic, something like As for this problem, it’s hard to solve.

Starting with Khó giải... is possible in special contexts, but it is less neutral and may sound literary or emphatic. For most learners, the original word order is the safest one to use.

giải has the hỏi tone.

A rough Northern pronunciation is close to zải. In Southern speech, gi may sound more like y or a soft j, depending on the speaker.

So the sentence is approximately:

• Vấn đề này khó giải
• Northern rough guide: vấn đề này khó zải

You do not need a perfect English-style approximation, but it helps to remember that giải here is one syllable with a dipping/rising tone in the North.