In the following sequence of reaction, the major products B and C respectively are:

Step 1: Reaction with Na/Et₂O (Wurtz coupling)

Cyclobutyl bromide + Na → Wurtz reaction → coupled product

$\ce{2 C4H7Br + 2 Na ->[Et2O] C4H7-C4H7 + 2 NaBr}$

Product A = Bicyclobutane (two cyclobutane rings joined)

Step 2: Grignard formation and deuterolysis

Product A + Mg in ether → Grignard reagent

Then reaction with $\ce{D2O}$ (deuterium oxide):

$\ce{R-Mg-R + D2O -> R-D + R-D + Mg(OD)2}$

This replaces the C-Mg bonds with C-D bonds.

Product B = Deuterated cyclobutane ($\ce{C4H7D}$)

Structure: Cyclobutane with D replacing H at the position where Br was originally.

Step 3: Reaction with CoF₂ (Swarts reaction)

Cyclobutyl bromide + $\ce{CoF2}$ → halogen exchange → fluoride

$\ce{C4H7Br + CoF2 -> C4H7F + CoBr2}$

Product C = Cyclobutyl fluoride

Structure: Cyclobutane with F at the position where Br was.

Answer: (a)

Key Reactions:

1. Wurtz coupling: $\ce{2 R-X + 2 Na -> R-R + 2 NaX}$
2. Grignard + D₂O: $\ce{R-MgX + D2O -> R-D}$ (deuteration)
3. Swarts reaction: $\ce{R-X + MF -> R-F}$ (halogen exchange to fluoride)

Note: Deuterium (D or ²H) is used as a tracer isotope of hydrogen.