In IUPAC nomenclature, preference is given to multiple bond than halogen substituent.

$$ \therefore $$ IUPAC name is trans-2-chloro-3-iodo-2-pentene.

Electron withdrawing group like -NO₂ facilitates nucleophilic substitution reaction in chlorobenzene.

In case of Lassaigne’s test of halogens, it is necessary to remove NaCN and Na₂S from the sodium extract, if nitrogen and sulphur are present. This is done by boiling the sodium extract with conc. HNO₃.

NaCN + HNO₃ $$ \to $$ NaNO₃ + HCN $$ \uparrow $$

Na₂S + 2HNO₃ $$ \to $$ 2NaNO₃ + H₂S $$ \uparrow $$