Obstawiam tę odpowiedź, ale mam wątpliwość.

In this sentence, obstawiam is being used in a colloquial sense: I’m going with, I’m betting on, or I’m guessing this answer.

It does not have to mean literal gambling. Polish speakers often use obstawiać when they choose the option they think is probably correct.

Yes. Obstawiam is the 1st person singular present tense of the imperfective verb obstawiać.

So it literally means I bet / I’m betting / I’m going with.

Its perfective partner is obstawić. The future form would be obstawię, for example: Obstawię tę odpowiedź = I’ll go with this answer / I’ll bet on this answer.

Because odpowiedź is the direct object of the verb obstawiam, so it must be in the accusative case.

• ta odpowiedź = nominative, used for the subject
• tę odpowiedź = accusative, used as the object

So:

• Ta odpowiedź jest dobra. = This answer is good.
• Obstawiam tę odpowiedź. = I’m going with this answer.

Because many native speakers use tą in everyday speech where standard grammar expects tę.

For a learner, the safest rule is:

• standard written Polish: tę odpowiedź
• very common colloquial speech: tą odpowiedź

In careful, standard Polish, tą is properly the instrumental form, as in z tą odpowiedzią = with this answer.

So if you are learning correct standard Polish, use tę odpowiedź.

Because odpowiedź is one of those feminine nouns whose nominative and accusative singular look the same.

So although the phrase changes case, the change is visible in tę, not in odpowiedź itself.

• nominative: ta odpowiedź
• accusative: tę odpowiedź

The noun stays odpowiedź in both forms.

It is accusative singular.

Why? Because it is the direct object of obstawiam: you are betting on / choosing that answer.

• verb: obstawiam
• object: tę odpowiedź

Not exactly. Tę is a form of the demonstrative pronoun ten / ta / to, so it means this.

Polish does not have articles like English the or a. So tę is not an article; it is a demonstrative word pointing to a specific answer.

Because in Polish, ale normally introduces another clause and is preceded by a comma.

So:

• Obstawiam tę odpowiedź, ale mam wątpliwość.

This is standard punctuation. It works much like a comma before but in English when two clauses are joined.

It is also accusative singular, because it is the direct object of mam.

• mam co? → wątpliwość

Just like with odpowiedź, the form wątpliwość looks the same in nominative and accusative singular.

It is grammatically correct, but it sounds a bit less natural than mam wątpliwości in many everyday contexts.

The difference is:

• mam wątpliwość = I have a doubt / one specific reservation
• mam wątpliwości = I have doubts / I’m not fully sure

In ordinary speech, Polish speakers very often prefer the plural:

• Obstawiam tę odpowiedź, ale mam wątpliwości.

So your original sentence is correct, but the plural version is often more idiomatic.

Yes. Polish word order is fairly flexible, and changing it usually changes emphasis rather than basic meaning.

Neutral order:

• Obstawiam tę odpowiedź, ale mam wątpliwość.

Possible emphatic order:

• Tę odpowiedź obstawiam, ale mam wątpliwość.

That version emphasizes this answer. For learners, the original order is the most neutral and safest to use.