for i in n:
if i % 2 != 0:
This is your code ,lets see what your code does.
1. Your function purify takes a list.
2. It loops through each item of your list.
3. It checks if item is odd or not.
4. If it is odd then it removes item from list.
Now lets read what question is asking--
Define an empty list.
And as it says not to change original list, leave the old list.
What you do now?
You check for even numbers and append them in new list ?
The last part tho (The returning) ,I'm leaving upto you.
I hope it helps!