Subject

Chemistry

Class

NEET Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

51.

SN2 reaction readily occurs in

  • CH3CH2-O-CH3

  • CH3-C(CH3)2-O-CH3

  • CH2=CH-CH2-O-CH3

  • Ph-CH2-O-CH2-CH3


A.

CH3CH2-O-CH3

SN2 reaction readily occurs in CH3CH2-O-CH3.


52.

Maximum decarboxylation occurs in

  • CH3COOH

  • C6H5COOH

  • C6H5CH2COOH

  • CH3COCH2COOH


D.

CH3COCH2COOH

CH3COCH2COOH is aβ-keto acid.Thus, decarboxylation is maximum in a carboxylic acid containing an electron withdrawing group such as -CO or -COOH at theβ- carbon atom with respect to the -COOH group.


53.

Assertion : Toluene in presence of UV rays forms benzaldehyde.

Reason : Dichlorotoluene is formed as an intermediate.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false.


D.

If both assertion and reason are false.

Oxidation of toluene using CrO3 in acetic anhydride or CrO2Cl2 in CCl4 or CS4 and then hydrolysis gives benzaldehyde. No such intermediate is formed.


54.

Assertion : Fructose is a reducing sugar.

Reason : It has a ketonic group.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false.


B.

If both assertion and reason are true but reason is not the correct explanation of assertion

All those carbohydrates which contain aldehydic or ketonic group in the hemiacetal or hemiketal form and reduce Tollen's or Fehling's solutions are reducing sugars. All monosaccharides are reducing sugars (whether aldoses or ketoses). Fructose is a monosaccharide with keto group


55.

Assertion: Dehydration of alcohols always takes place in basic medium.

Reason : OH- is a better leaving group.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false.


D.

If both assertion and reason are false.

Dehydration of alcohols can be carried out either with protonic acids such as conc. H2SO4, H3PO4 or catalysts such as anhydrous zinc chloride or alumina.


56.

The correct increasing order of reactivity for the following molecules towards electrophilic aromatic substitution is

  • I < IV < II < III

  • I < IV < II < IV

  • I < III < II < IV

  • I < III < IV < II


B.

I < IV < II < IV

The correct increasing order of reactivity is I < IV < II < III. This is because greater is the electron density on aromatic ring, greater is the reactivity towards electrophilic aromatic substitution.


57.

The correct decreasing order of pKa is

  • II > IV > I > III

  • IV > II > III > I

  • III > II > IV > I

  • IV > I > II > III


A.

II > IV > I > III

The correct decreasing order of pKa is II > IV > I > III.

Weaker acids have higher pKa - OCH3 atmeta-position exerts only -I effect, hence, it increases the acidity.

-I effect order : -NO2 > -OCH3 > -Cl

-CH3 has +I effect.


58.

The corrcet decreasing order of pKb is

  • I > II > III > IV

  • III > IV > II > I

  • II > III > IV > I

  • IV > II > I > III


D.

IV > II > I > III

The correct order of pKb is IV > II > I > III. This is because substituent with strong +R effect, +I effect and weaker -I effect increases the basicity. Hence pKb decreases. Also, alkylamines are stronger bases than arylamines.


59.

Assertion : p-Nitrophenol gives more electrophilic substituted compound than m-methoxyphenol.

Reason : Methoxy group shows only negative I-effect.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false.


D.

If both assertion and reason are false.

In p-nitrophenol, - NO2 group has -I effect, as a result of which electron density decreases on the benzene ring, hence reactivity towards electrophilic substitution decreases. Methoxy group shows both +R (due to lone pair of electrons on O) and -I effect (due to greater electronegativity of O).

OCH3 at meta-position shows only -I effect but lesser than -I effect of -NO2 group.


60.

Assertion : β-pleated sheet structure of protein shows maximum extension.

Reason : Intermolecular hydrogen bonding is present in them.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false


B.

If both assertion and reason are true but reason is not the correct explanation of assertion

In β-pleated sheet structure, the polypeptide chains are held together by intermolecular H-bonds. Extension and contraction of β-pleated sheet structure of protein depends on the size of R.