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CBSE Class 12 Pre Board 2021 : Chemistry (Kendriya Vidyalaya (KV) No 1, Armapur, Kanpur)

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PRE-BOARD Examination - 2020-21 Time 1. 2. 3. 4. 5. Q.1. 3 Hours Subject - Chemistry Class - XII M.M.- 70 Instruction : There are 33 questions in this question paper. All questions are compulsory. Section A : Question number 1 and 2 are case based questions having four MCQs or Assertion-Reason type based on given passage each carrying 1 mark and questions 3 to 16 are MCQs and Assertion-Reason type questions carrying 1 mark each. Section B : Question number 17 to 25 are short answer type I questions and carry 2 marks each. Section C : Question number 26 to 30 are short answer type II questions carrying 3 marks each. Section D : Question number 31 to 33 are long answer questions carrying 5 marks each. Section - A Passage based questions : Read the passage given below and answer the following questions : Elimination and substitution reactions can occur simultaneously. When alkyl halide reacts with nucleophile, it may undergo either substitution via SN1 and SN2 or elimination reaction. It depends upon the nature of alkyl halide, strength and size of nucleophile, conditions of the reaction. Primary alkyl halide will prefer SN2 reaction i.e., nucleophilic substitution reaction via SN2 mechnaism. Secondary alkyl halide can undergo substitution or elimination depending upon the strength of the nucleophile. Stronger nucleophile like OC2H5 will bring out elimination whereas nucleophiles like OH will bring out substitution. Tertiary alkyl halide will undergo substitution or elimination depending upon stability of carbocation or the more substituted alkene. The following questions (i - iv) are multiple choice questions. Choose the most appropriate answer : (i) When ethyl chloride is treated with aq, KOH we get : (a) methanol (c) ethanoic acid (b) ethanol (d) ethanol (ii) Which of the following would undergo SN2 reaction faster? (a) CH3 CH2 Br (c) (CH3)3 C Br (b) CH3 CH Br CH3 (d) None of these (iii) Racemisation will take place in : (a) SN1 reaction (c) climination reaction (b) SN2 reaction (d) None of these (iv) The product formed in the following reaction : XII - Chemistry (1) P.T.O.

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