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In the Duolingo courses I came across the sentence:

`この言葉の意味を答えてください。`

translated as:

`Please tell me the meaning of this word.`

The thing is 答える is an intransitive verb (自動詞); and in other sentences things
like 質問に答える are being used.

So the question about why on that particular sentences it uses を...

I am familiar with the use of を for intransitive verbs of _motion_.

  * 学校に行く : to go to school (に marks the purpose, the goal)
  * 公園を歩く: to walk in(across) the park (を marks the medium by which the walking is done)

So I suppose it is something similar:

  * 質問に答える : answer to a question (に marks the purpose, the goal)
  * 意味を答える : answer "with/by" a meaning (を marking the "medium" by which the answering is done: trough the meaning) 

Note that that last point is just a speculation of mine.  
While there are various examples of ~を答える to be found, even in dictionaries; I
haven't seen so far an explanation of it (for 答える; for verbs of motion yes, a
lot), and so I am not fully confident my interpretation is correct.  
Advice from a native speaker of more knowledgeable would be welcome.
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2020-02-07T22:43:43.823
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2020-02-08T12:32:44.650
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question
grammar particle-を
is を答える similar to を歩く?
答える is a transitive verb, too.

明鏡国語辞典 says:

> こたえる【答える】  
>  〘 **他** 下一〙相手の質問などに対して、言葉を返す。返事をする。「問われるままにありのままを答えた」  
>  〘自下一〙問題を解いて答えを出す。解答する。「次の問いに答えよ」

So in your examples:

「質問 **に** 答える」 ← the 答える is intransitive  
「意味 **を** 答える」 ← the 答える is transitive

* * *

As a side note, verbs that can be both transitive and intransitive include:

[開]{ひら}く -- 「ドアが開く」「傘を開く」  
[閉]{と}じる -- 「つぼみが閉じる」「目を閉じる」  
[終]{お}わる -- 「戦争が終わる」「授業を終わる」  
[増]{ま}す -- 「食欲が増す」「水かさを増す」  
[引]{ひ}く -- 「腫れがひく」「辞書をひく」  
[吹]{ふ}く -- 「風が吹く」「笛を吹く」  
[触]{ふ}れる -- 「脈が触れる」「手を触れる」  
etc.
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2020-02-08T02:49:39.953
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2020-02-08T12:32:44.650
2020-02-08T12:32:44.650
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answer