Correct answer is 4. Show all the steps involved in detail.

  Q4. ${\mathrm{CaC}}_2\stackrel{{\mathrm{H}}_2\mathrm{O}}{\to }\mathrm{A}\underset{{\mathrm{NH}}_4\mathrm{Cl}}{\overset{{\mathrm{Cu}}_2{\mathrm{Cl}}_2}{\to }}\mathrm{B}\underset{\underset{ \left(3\right) {\mathrm{CO}}_2/{\mathrm{H}}_2\mathrm{O}/{\mathrm{H}}^{+}}{\left(2\right) \mathrm{Mg}/\mathrm{ether}}}{\overset{\left(\mathrm{I}\right)1\mathrm{equ}.\mathrm{HCl}}{\to }}\mathrm{C}$ 

       In above reaction product (C) is 

    (1) CH₂ = CH – COOH

    (2) HC $\equiv$C –– COOH

    (3) HOOC –– C$\equiv$C ––COOH

    (4) CH₂ = CH – C = CH₂
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                              COOH