Central Board Of Secondary Education [CBSE] — Facing some issues in answer key of term 1 science paper issued by cbse

I am a student of class 10 .I and my classmates are having some confusions in the answer key of term 1 science examination.In question no.28 correct option is not given only but in answer key answer is given c .It is wrong because in bracket minus (-) sign is not given so it should be a bonus question for all.Alsoin question no. 31 correct answer is A but in answer key B is given.
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