Subject

Chemistry

Class

NEET Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

41.

Which one of the following statements is not true? 

  • In vulcanization, the formation of sulphur bridges between different chains make rubber harder and stronger

  • Natural rubber has the trans-configuration at every double bond

  • Buna-S is a copolymer of butadiene and styrene

  • Buna-S is a copolymer of butadiene and styrene


B.

Natural rubber has the trans-configuration at every double bond

Natural rubber is cis-polyisoprene nd is prepared from latex which is obtained from the rubber tree.

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42.

Acetophenone when reacted with a base, C2H5ONa, yields a stable compound which has the structure


A.

Aldehydes or ketones with the alpha-H atom, in presence of the dilute base, undergoes aldol condensation to give Beta-hydroxy aldehyde or beta-hydroxy ketone. On heating, aldol eliminates water molecule to form alpha, beta unsaturated compound.

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43.

In DNA. the complimentary bases are 

  • Adenine and thymine; guanine and cytosine

  • Adenine and thymine; guanine and uracil

  • Adenine and guanine, thymine: Guanine and uracil

  • Adenine and guanine, thymine: Guanine and uracil


A.

Adenine and thymine; guanine and cytosine

Deoxyribonucleic acid (DNA) has the purine bases adenine and guanine and pyrimidine bases thymine and uracil. According to base pairing rule adenine paired with thymine (A=T) and cytosine paired with guanine straight C identical to straight G 

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44.

Which one of the following is an amine hormone?

  • Thyroxine

  • Oxypurin

  • Insulin

  • Progesterone


A.

Thyroxine

The hormone which is proteinous nature are said to be amine hormone because protein is the polymers of polypeptides and polypeptides are made up of amino acids. An amino acid contains amino group.

Thyroxin is an amine hormone. It is secreted by the thyroid gland. Its function is to control the metabolism of carbohydrates, proteins and lipids.

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45.

In an SN2  substitution reaction of the type which straight R minus Br space plus space Cl to the power of minus space rightwards arrow with DMF on top space straight R minus space Cl space plus space Br to the power of minus one of the followings has the highest relative rate?

  • CH3-CH2-CH2Br

  • CH3-CH(CH2)-CH2Br

  • CH3C(CH3)2CH2Br

  • CH3C(CH3)2CH2Br


D.

CH3C(CH3)2CH2Br

The relative reactivity of alkyl halide towards SN N reactions is as follows;
Primary > secondary > Tertiary
However, if the primary alkyl halide or the nucleophile/base is sterically hindered the nucleophile will have difficulty to getting the back side of the alpha carbon as a result of this elimination product will be predominant. Here CH3CH2Br is the least hindered, hence it has the highest relative rate towards SN2 reaction.

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46.

The relative reactivities of acyl compounds towards of nucleophilic substitution are in the order of 

  • Acyl chloride> Acid anhydride> Ester> Amide

  • Ester > Acyl chloride> Amide > Acid anhydride

  • Acid anhydride > Amide > Ester> Acyl chloride

  • Acid anhydride > Amide > Ester> Acyl chloride


A.

Acyl chloride> Acid anhydride> Ester> Amide

The ease of nucleophilic substitution is depended upon the nature of leaving the group. When the leaving tendency of a group in a compound is high, then the compound is more reactive towards nucleophilic substitution.
The nucleophilic acyl substitution is completed in two-step as shown below.


The reactivity of the compound may be explained on the basicity of the leaving group. A weaker base is a better leaving group. The basicity order is as:
Cl- < RCOO- < RO- < NH-2
Hence, the order of leaving tendency is

Cl- > RCOO- > RO-> NH-2
and therefore, the order of reactivity of acyl compounds is as:

Acyl chloride >Acid ayhdride > Ester > Amide
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47.

A ( Predominantly) is

B.

The mechanism of electrophilic addition reaction is consistent with the occurrence of rearrangement leading to more stable carbocation.

The order of stability of carbocation is as;

T > S> P > CH3

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48.

In a reaction of aniline, a coloured product C was obtained.



D.

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49.

which one of the following is most reactive towards electrophilic attack? 



C.

Electron releasing groups stabilise the intermediate cation whereas electron withdrawing groups destabilise it.
The order of electron withdrawing group is:

NO2 > Cl >OH> C6H5
Hence is more reactive towards electrophilic substitution because -OH group least destabilise the carbocation. Further -OH group is strongly activating group while -NO2 and -Cl are deactivating group.

480 Views