Which of the following statement is correct in relation to the halogenation of alkane?

Which of the following is correct potential energy diagram for the given chain propagating step?

Identify the major product.

Electrochemical oxidation of the succinate ion $(1, 4-\mathrm{butanedioate} \mathrm{ion})$ into ethylene proceeds through the formation of the intermediate

By which reagents alkyne converts to trans alkene and then to dibromobutane? i.e., ${\mathrm{CH}}_3-\mathrm{C}\equiv \mathrm{C} - {\mathrm{CH}}_3\stackrel{\mathrm{R}}{\to } \stackrel{\mathrm{S}}{\to }{\mathrm{C}}_4{\mathrm{H}}_8{\mathrm{Br}}_2 \left(\mathrm{Achiral}\right)$

$\mathrm{R} \text{and} \mathrm{S}$ are, respectively:

Which of the following is the product?