For now, the motion institute has released the unofficial answer key for class 5 to 10. The official answer keys will be released soon by January 2020.
You can get the answer keys of 2018 for class 4 from the link given below:
Hope this helps!
You can get class 4 answer key of NCO 2019 for both SET A and B by going through our page for which link is provided below :-
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