Explain with equations: (i) dehydrohalogenation and Zaitsev's rule, (ii) the Wurtz reaction, (iii) the preparation of a Grignard reagent, and why it must be kept dry.

1. 1 · Define elimination. In β-elimination, H from the β-carbon and X from the α-carbon are removed, giving an alkene.
2. 2 · Zaitsev example.
   • CH₃CH₂CH₂CH(Br)CH₃ + KOH (alc) → pent-2-ene (major) + pent-1-ene (minor)
   • Rule: the more substituted alkene is the major product
3. 3 · Wurtz reaction. 2CH₃Br + 2Na (dry ether) → CH₃-CH₃ + 2NaBr.
4. 4 · Grignard reagent. CH₃CH₂Br + Mg (dry ether) → CH₃CH₂MgBr.
5. 5 · Why it must be dry. CH₃CH₂MgBr + H₂O → CH₃CH₃ + Mg(OH)Br; any proton source destroys the reagent.
6. 6 · Close in one line. So the reagent and solvent decide whether a haloalkane gives an alcohol, an alkene or a new C-C bond.

Scoring tip: Write 'alcoholic' or 'dry ether' above the arrow; without it the equation loses a mark.