Which one is correct?
The (ending/end) of the film was so predictable.

Question

Answer

Either is OK.  Ending is more specific and is used to describe the end of a story.  You would say "end of the road" but never "ending of the road."  But either is one is OK for books, movies, etc

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The appropriate word used is "climax" of the film.

if u want any one from ending /end i would say as end rather than ending

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The ending of the film would be the last part. The end of the film would be when you get up and leave.