unbeantwortet
unanswered
Describes a question, letter, or message to which no answer has been given.
Seine E-Mail blieb eine Woche lang unbeantwortet.
His email went unanswered for a week.

unanswered
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unanswered
Describes a question, letter, or message to which no answer has been given.
Seine E-Mail blieb eine Woche lang unbeantwortet.
His email went unanswered for a week.

'Unbeantwortet' (unanswered) is formed from the prefix 'un-' and the past participle 'beantwortet' (answered), from 'beantworten' (to answer). So it describes a state in which something has not been answered.
Leider sind noch viele meiner Fragen unbeantwortet.
Unfortunately, many of my questions are still unanswered.
'Unbeantwortet' (unanswered) is very frequently used together with the verb 'bleiben' (to remain). This construction emphasizes that a state continues over a certain period of time.
Seine Bitte um Hilfe blieb leider unbeantwortet.
His request for help unfortunately remained unanswered.
In this meaning, 'unbeantwortet' (unanswered) refers to direct communication. Typical nouns are 'Frage' (question), 'E-Mail' (email), 'Brief' (letter), 'Nachricht' (message), or 'Anruf' (call).
Ich habe drei unbeantwortete Anrufe von meiner Chefin auf dem Handy.
I have three unanswered calls from my boss on my phone.
When it is about major, often scientific or philosophical topics, 'unbeantwortet' (unanswered) means something like 'unsolved' or 'unresolved'. It then describes a still-existing mystery or problem.
Die Frage nach Leben auf anderen Planeten ist bislang unbeantwortet.
The question of life on other planets remains unanswered so far.
open
'offen' and 'unbeantwortet' can both mean that something has not yet been clarified. 'offen' is broader: a question, point, or decision is still open if there is not yet a solution or decision. 'unbeantwortet' fits especially with questions, letters, messages, or problems to which no answer has been given yet. Learners may confuse the words because an open question is often also unanswered. The difference is: 'offen' emphasizes the unresolved state, while 'unbeantwortet' emphasizes the missing answer.

Meine E-Mail an die Verwaltung ist seit drei Tagen unbeantwortet.
My email to the administration has gone unanswered for three days.
Nach dem Gespräch blieb noch eine wichtige Frage offen.
After the conversation, one important question remained open.