Give main product of the following reaction. (in one step)
(i) 1, 2-dibromo propane + alcoholic KOH
(ii) 1, 1, 2,2-tetrabromo ethane + zinc powder in methanol
(iii) 1,1,2,2-tetrabromo propane + zinc powder in methanol.
(iv) Reaction occur on passing of hydrogen gas through carbon electrode at high temperature in electric arc.

Explanation

(iii) `underset("1,1,2,2-tetrabromo propane")(CH_(3)CBr_(2)CHBr_(2) + 2Zn) rarr underset("Propyne")(CH_(3)C)-=CH+2ZnBr_(2)`
(iv) `2C+H_(2) underset(3270K)overset("Electric arc")rarr HC -= CH`