Hydrocarbons MCQs for NEET — Chemistry Questions with Answers

The NCERT text states: 'Thus the absence of pure double bond in benzene accounts for the reluctance of benzene to show addition reactions under normal conditions, thus explaining the unusual behaviour of benzene.' This 'absence of pure double bond' is due to the delocalized $\pi$ electron system, which contributes to its enhanced stability. Therefore, option o3 is the correct explanation.

The NCERT text provides a list of common names: 'Methylbenzene (Toluene)'. Therefore, option o3 is correct.

The NCERT text says: 'Substituent of the base compound is assigned number 1 and then the direction of numbering is chosen such that the next substituent gets the lowest number.' This clarifies the numbering rule, making option o2 correct.

The NCERT text clearly states: 'For tri- or higher substituted benzene derivatives, these prefixes cannot be used and the compounds are named by identifying substituent positions on the ring by following the lowest locant rule.' Hence, option o3 is correct.

The NCERT text states: 'When a benzene ring is attached to an alkane with a functional group, it is considered as substituent, instead of a parent. The name for benzene as substituent is phenyl (C6H5-, also abbreviated as Ph).' Therefore, 'phenyl' is the correct name.

The NCERT text mentions: 'Aromatic hydrocarbons, despite having unsaturation, undergo mainly electrophilic substitution reactions. These undergo addition reactions only under special conditions.' This highlights the predominant reaction type for aromatic hydrocarbons, making option o3 correct.

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

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 mol–1 due to weak repulsive interaction between the adjacent bonds. Such a type of repulsive interaction is called torsional strain.' (Chapter: Hydrocarbons, Page 305)

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

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)