$2-$butyne is reduced to $trans-but-2-ene$ using:

The final major product obtained in the following sequence of reaction is

Which alkyne yields butanoic acid $(CH_3CH_2CH_2CO_2H)$ as the only organic product on treatment with ozone followed by the hydrolysis?

$But-1-yne$ reacts with cold alkaline $KMnO_4$ to produce:

$CH_3 - C \equiv C - CH_3 \xrightarrow[CH_3COOH]{BH_3, THF} \text{Major product}$

The reagent used in the reaction $R-CH_2-CCl_2-R \xrightarrow{\text{Reagent}} R-C \equiv C-R$ is .............