How does bromine solution in ${\mathrm{CCl}}_4$ helps to distinguish alkanes and alkenes?

Column I         

Column II

(i)

${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH} \underset{{300}^{\mathrm{o}}\mathrm{C}}{\overset{{\mathrm{Al}}_3{\mathrm{O}}_3}{\to }}$

(a)

Ethane

(ii)

${\mathrm{C}}_2{\mathrm{H}}_4 + {\mathrm{H}}_2 \underset{\mathrm{Ni}}{\overset{{200}^{\mathrm{o}}\mathrm{C}}{\to }}$

(b)

Ethyne

(iii)

$\mathrm{Br}-{\mathrm{CH}}_2-{\mathrm{CH}}_2-\mathrm{Br} + \mathrm{alc}.\mathrm{KOH} \stackrel{\mathrm{Boil}}{\to }$

(c)

Ethyl hydrogen sulphate

(iv)

${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH} + {\mathrm{H}}_2{\mathrm{SO}}_4\to$

(d)

Ethene

Column I

Column II

(i)

Alkane

(a)

${\mathrm{C}}_2{\mathrm{H}}_{2\mathrm{n}+2}$ 

(ii)

Alkene

(b)

${\mathrm{C}}_2{\mathrm{H}}_{2\mathrm{n}-2}$ 

(iii)

Alkyne

(c)

${\mathrm{C}}_2{\mathrm{H}}_{2\mathrm{n}}$