Class 12 Chemistry (NCERT)

1. Haloalkanes readily undergo nucleophilic substitution reactions mainly because:

• A. The carbon-halogen bond is polar, with the carbon bearing a partial positive charge
• B. They are completely non-polar
• C. The halogen has very low electronegativity
• D. They lack any lone pairs

2. SN1 reactions proceed through the formation of a(n):

• A. Carbocation intermediate
• B. Concerted transition state without intermediate
• C. Free radical intermediate
• D. Direct one-step substitution

3. Tertiary alkyl halides predominantly react via the:

• A. SN1 mechanism
• B. SN2 mechanism
• C. Elimination only, never substitution
• D. Addition mechanism

4. Which of the following alkyl halides shows the highest reactivity towards the SN2 mechanism?

• A. CH3Br
• B. (CH3)3CBr
• C. (CH3)2CHBr
• D. CH3CH2CH(CH3)Br

5. A Grignard reagent is prepared by reacting a haloalkane with:

• A. Magnesium metal in dry ether
• B. Sodium metal in wet ether
• C. Zinc metal in water
• D. Copper metal in ethanol

6. Chlorobenzene is less reactive than an alkyl halide towards nucleophilic substitution mainly because:

• A. Resonance gives the C-Cl bond partial double bond character, strengthening it
• B. Chlorine has an unusually high electronegativity
• C. It has no lone pairs on chlorine
• D. Of steric hindrance alone

7. Freons (chlorofluorocarbons) are mainly used as:

• A. Refrigerants and aerosol propellants
• B. Insecticides
• C. Solvents for polymerization
• D. Anesthetics

8. DDT is chemically known as:

• A. Dichlorodiphenyltrichloroethane
• B. Dichlorodifluoromethane
• C. Trichloroethylene
• D. Tetrachloroethane

9. Treatment of haloalkanes with alcoholic KOH predominantly gives:

• A. Alkenes, through an elimination reaction
• B. Alcohols
• C. Ethers
• D. Alkanes

10. Racemization is most commonly observed in reactions proceeding through the:

• A. SN1 mechanism
• B. SN2 mechanism
• C. Simple addition reactions
• D. Free radical halogenation only

11. Which type of halide is generally most reactive towards the SN1 mechanism?

• A. Tertiary halide
• B. Primary halide
• C. Methyl halide
• D. Vinyl halide

12. The iodoform test is used to detect the presence of:

• A. A CH3CO- group, or a CH3CH(OH)- group that can be oxidized to it
• B. A -COOH group
• C. A -OH group in any alcohol
• D. A -CHO group only