The electrophile. E^$\oplus$ attacks the benzene ring to generate the intermediate $\mathrm{\sigma }$- complex. Of the following which $\mathrm{\sigma }$- complex is of lowest energy?

1. 

2. 

3. 

4. 

Consider the following bromides:

the correct order of S_N1 reactivity is:

1. A>B>C

2. B>C>A

3. B>A>C

4. C>B>A

KI in acetone, undergoes S_N2 reaction with each of P, Q, R and S, the rates of the reaction vary as:

1. P > Q > R > S

2. S > P > R > Q

3. P > R > Q > S

4. R > P > S > Q

In an S_N1 reaction on chiral centres there is

1. 100% racemisation

2. inversion more than retention leading to partial racemisation

3. 100% retention

4. 100% inversion

If X is halogen the correct order for S_N2 reactivity is-

1. R₂CHX > R₃CX > RCH₂X

2. RCH₂X > R₃CX > R₂CHX

3. RCH2X > R₂CHX > R₃X

4. R₃CX > R₂CHX > RCH₂X

The compound which reacts with HBr obeying Markownikoff's rule is:

1. $C{H}_2=C{H}_2$   

2. 

3. 

4. 

The formation of cyanohydrin from a ketone is an example of:

(1) electrophilic addition

(2) nucleophilic addition

(3) nucleophilic substitution

(4) electrophilic substitution

Which of the following is an example of the elimination reaction?

(1) Chlorination of methane

(2) dehydration of ethanol

(3) nitration of benzene

(4) hydroxylation of ethylene

The S_N2 mechanism for R-X + KOH (aq) $\to$ R-OH + KX follows with:

(1) 100% inversion

(2) 50% inversion

(3) 40% inversion

(4) 30% inversion

The elimination reaction among the following is:

1. CH₃CH₃+Cl₂$\to$CH₃CH₂Cl+ HCl

2. CH₃Cl+ KOH(aq.) $\to$CH₃OH +KCl

3. CH₂=CH₂ +Br₂ $\to$CH₂BrCH₂Br

4. C₂H₅Br+ KOH(alc.) $\to$C₂H₄ + KBr+H₂O