The stereoisomers that are formed by electrophilic addition of bromine to trans-but-2-ene is/are :

For the following sequence of reactions, the correct products are :

The correct sequence of correct reagents for the following transformation is :

Presence of which reagent will affect the reversibility of the following reaction, and change it to a irreversible reaction :

CH₄ + I₂ $$\mathrel{\mathop{\kern0pt\rightleftharpoons} \limits_{{\mathop{\rm Re}\nolimits} versible}^{hv}} $$ CH₃ $$-$$ I + HI