Por or Para with quien?

Question

Slightly confused here. The text suggests "para" but the answer says "por"

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Hola William
Are you referring to this specific question from the test?
¿___ arriesgarías tu vida? (Who would you risk your life for?)
Correct answer: "¿Por quién.....?
Inma

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Yes, I was referring to this specific question. Can you give advice on when to use "Para" and when to use "por" with "quien"?
Thanks in anticipation.

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Sorry this reply is six months late, but I hope it still helps!
From what I've seen and read, "para quién" seems to be used when some material object is to be given to someone. E.g. ¿Para quién has comprado esas flores?  Or ¿Para quién es el café con leche? 
Whereas if this is not the case, and "for" really means "for the sake of" or "on behalf of", then "por quién" is used. E.g. ¿Por quién harías una locura? Or "¿Por quién arriesgarías tu vida?
Hope this is not misleading.

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We don't seem to have a definitive answer from KWIZIQ TEAM for the distinctikon between "¿Para quién?" y "¿por quién?"  The latter also translates as "by whom"

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I also was hoping for some guidance on when por quién is appropriate vs. para quién.

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Here is my take on "por" or "para"If you go to the shop to buy something, "para" someone, you are paying for it and buying it as a gift for example.If you go to buy the same item "por" someone, the someone is paying for it and you are going to the shop on their behalf because they don't have the time or they are incapacitated.In the same vein, you could do something for someone and they benefit from what you do OR you could do something on their behalf for soemone else and the someone else benefits from the work you do.  Para and por inb that order.

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I think I understand now. The guy on Language Transfer explained it with these examples.

Compré un cenicero para usted. The friend takes the ashtray away.

Compré un cenicero por usted. The friend only uses the ashtray in my house. It is my ashtray.

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Hi all, 
sorry, I think the follow up comments after Williams first initial question must have fallen through the cracks (no notifications for some reason).
As you all probably know, por and para have specific uses, there is not one general rule to differentiate them. This is why in Kwiziq we have lots of different lessons on each depending on the very specific context and meaning. As in English there is only one: "for", sometimes it is a bit difficult to see what exactly we mean using that por or that para. At the end of the messsage you will find a link with general information about por and para and a list of lessons by the end for each specific use.
Going back to the first sentence mentioned in this thread using "por quién":

¿Por quién arriesgarías tu vida?
Who would you risk your life for?

This "por" means "a reason", a "because of whom". 
If we use an affirmative sentence without "quién" it is easier to see:

Yo arriesgué mi vida por ti. 
I risked my life for you / because of you. (You were the reason why I risked my life)

It wouldn't make much sense to use "para" here. 
Yo arriesgué mi vida para ti. (??)
"Para" would have to indicate that that person is the recipient of something, the destination of something...; so these meanings wouldn't make sense here. 
Here is the link to our different lessons on por and para:
Por and Para
Saludos
Inma

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Thanks Inma. I understand it better now.