Q1.When two hydrogen atoms in benzene are replaced by two similar or different monovalent atoms or groups, how many different position isomers are possible?
Answer : Option CExplaination / Solution:
the three isomers will be ortho(i.e.1,2- or 1,4-disubstituted) , meta(i.e.1,3- or 1,5-disubstituted) and para(1,4-disubstituted)
Q2.The unusual behavior of benzene is explained by
Answer : Option DExplaination / Solution:
resonance stabilisation explains the unusual stability of benzene.There is pi electron delocalisation in the ring which enhances the stability of the molecule.
Q3.Aromatic compounds are charachterized by the presence of _____ π electrons in the ring where n is an integer (n = 0, 1, 2, . . .).
Answer : Option DExplaination / Solution:
Huckel rule which explains the unusual stability of cyclic conjugated polyenes(i.e. aromatic compounds) over other cyclic unsaturatrd compounds which do not contain (4n+2) pi electrons.
Q4.Which of the following method is not a synthetic method for production of Benzene?
Answer : Option AExplaination / Solution:
Since isolation of benzene from coal tar involves separation of benzene from other components through a physical operation "fractional distillation" , it is NOT a synthetic method for production of benzene.
Q5.In Friedel-Crafts alkylation reaction, when benzene is treated with an alkyl halide in the presence of a catalyst, alkylbenene is formed. The catalyst used is
Answer : Option AExplaination / Solution:
the acid chloride or anhydride reacts with anhydrous aluminium chloride to form the acylium ion which serves as an electrophile which then attacks the benzene ring to give alkylbenzene.
Q7.Arrange the following in decreasing order of their boiling points. (A) n–butane (B) 2–methylbutane (C) n-pentane (D) 2,2–dimethylpropane
Answer : Option CExplaination / Solution:
Boiling point depends on molecular mass and surface area.As the number of carbon atoms increase,boiling point increases ,hence n-butane has the minimum boiling point.Among isomeric alkanes,boiling point decreases with branching.Hence the order.
Arrange the halogens F2, Cl2, Br2,I2,in order of their increasing reactivity with alkanes.
Answer : Option CExplaination / Solution:
The reaction follows free radical mechanism in which the first step is generation of halogen free radical which is the fastest for fluorine.Hence the order.
Q9.The increasing order of reduction of alkyl halides with zinc and dilute HCl is
Answer : Option CExplaination / Solution:
As we move from I to Br to Cl,atomic size decreases,it becomes difficult to release the halogen as the bond length decreases.Hence I- is the best leaving group among halogens and reacts the fastest.