The reaction of $1,1,2,2$-tetrabromoethane with zinc dust produces .............

When propyne reacts with aqueous $H_2SO_4$ in the presence of $HgSO_4$,the major product is

What is the product formed when $4$-octyne reacts with $H_2$ in the presence of $Pd/CaCO_3$?

Which reaction converts $2$-hexyne into $trans$-$2$-hexene?

To convert $1$-butyne to $1-D$-butanal,one would carry out the following steps :
$(I)$ Sodium amide,then $D_2O$
$(II)$ Disiamylborane,then hydrogen peroxide/sodium hydroxide
$(III)$ The transformation can not be carried out with the indicated reagents.

At low temperatures,the slow addition of molecular bromine to $CH_2=CH-CH_2-C \equiv CH$ gives: