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NEET Practice Questions (MCQs) with Answers & Solutions

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How does the s-character of the carbon hybrid orbital in the C-X bond affect its strength in haloarenes compared to haloalkanes?

A. Lower s-character in haloarenes leads to a weaker and longer bond. B. Higher s-character in haloarenes leads to a stronger and shorter bond. C. S-character has no influence on bond strength. D. Higher s-character in haloarenes leads to a weaker and shorter bond.

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Explanation

The sp$^2$ hybridised carbon with a greater s-character (in haloarenes) is more electronegative and can hold the electron pair of the C-X bond more tightly than sp$^3$-hybridised carbon (in haloalkanes) with less s-character. This results in a stronger and shorter bond in haloarenes.

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What is the consequence of the C-X bond acquiring partial double bond character in haloarenes regarding bond cleavage?

A. It makes the bond easier to cleave. B. It makes the bond cleavage more difficult. C. It has no effect on bond cleavage. D. It leads to heterolytic cleavage only.

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Explanation

C-Cl bond acquires a partial double bond character due to resonance. As a result, the bond cleavage in haloarene is difficult than haloalkane and therefore, they are less reactive towards nucleophilic substitution reaction.

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Which of the following describes the electron distribution around the internuclear axis of a C-C sigma bond in alkanes?

A. Symmetrical and easily disturbed by rotation. B. Asymmetrical and not disturbed by rotation. C. Symmetrical and not disturbed by rotation. D. Asymmetrical and easily disturbed by rotation.

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Explanation

As per the NCERT text, 'Electron distribution of the sigma molecular orbital is symmetrical around the internuclear axis of the Câ€“C bond which is not disturbed due to rotation about its axis.' This symmetry allows for free rotation. (Chapter: Hydrocarbons, Page 305)

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The rotation around a C-C single bond in alkanes is not completely free due to a weak repulsive interaction between adjacent bonds, known as:

A. Steric hindrance B. Bond strain C. Torsional strain D. Angular strain

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Explanation

The context states: 'rotation around a C-C single bond is not completely free. It is hindered by a small energy barrier of 1-20 kJ molâ€“1 due to weak repulsive interaction between the adjacent bonds. Such a type of repulsive interaction is called torsional strain.' (Chapter: Hydrocarbons, Page 305)

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How many conformations can alkanes theoretically have by rotation around C-C single bonds?

A. Two B. finite, small number C. Three D. An infinite number

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Explanation

The NCERT text explicitly states: 'Alkanes can thus have infinite number of conformations by rotation around C-C single bonds.' (Chapter: Hydrocarbons, Page 305)

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In the ethane molecule ($C_2H_6$), which conformation has the hydrogen atoms attached to the two carbons as closed together as possible?

A. Staggered conformation B. Eclipsed conformation C. Skew conformation D. Anti conformation

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Explanation

The NCERT states: 'One such conformation in which hydrogen atoms attached to two carbons are as closed together as possible is called eclipsed conformation...' (Chapter: Hydrocarbons, Page 305)

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What is the typical energy barrier range (in kJ mol$^{-1}$) that hinders the completely free rotation around a C-C single bond in alkanes?

A. 1-1 kJ mol$^{-1}$ B. 20 kJ mol$^{-1}$ C. 50 kJ mol$^{-1}$ D. 100 kJ mol$^{-1}$

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Explanation

The NCERT text mentions: 'It is hindered by a small energy barrier of 1-20 kJ molâ€“1 due to weak repulsive interaction between the adjacent bonds.' (Chapter: Hydrocarbons, Page 305)

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Which of the following is NOT an alternative term for conformations?

A. Conformational isomers B. Rotamers C. Tautomers D. Spatial arrangements

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Explanation

The context defines conformations as 'spatial arrangements of atoms which can be converted into one another by rotation around a C-C single bond are called conformations or conformers or rotamers.' Tautomers are a different type of isomerism involving proton transfer and rearrangement of electrons. (Chapter: Hydrocarbons, Page 305)

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How is the front carbon atom represented in a Newman projection?

A. By a circle B. By a point C. By a longer straight line D. By a square

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Explanation

According to the NCERT description of Newman projections: 'The carbon atom nearer to the eye is represented by a point.' (Chapter: Hydrocarbons, Page 305)

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In a Sawhorse projection, the central C-C bond is depicted as:

A. point B. circle C. somewhat longer straight line D. curved line

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Explanation

The NCERT states for Sawhorse projections: 'It is then projected on paper by drawing the central Câ€“C bond as a somewhat longer straight line.' (Chapter: Hydrocarbons, Page 305)

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