Distinction between pairs of compounds
Ethane and Ethane or Acetylene.

Explanation

Ethane is a saturated hydrocarbon while ethene and acetylene are unstaturated hydrocarbons. These can be distinguished by the following tests:
(a) Bromine test . Ethene as well as acetylene decolourise solution of `Br_(2)` in carbon tetrachloride due to the reactions given below:

`H-underset("Acetylene")(C-=C)-H+undersetunderset("red")("Brownish")(Br_(2)//C Cl_(4))rarrBr-underset("Colourless")(overset(H)overset(|)(C)=overset(H)overset(|)(C))-Br`
`Br-oversetoverset(H)(|)(C)=oversetoverset(H)(|)(C)-Br+Br_(2)//C Cl_(4)rarrBr-undersetunderset(Br)(|)oversetoverset(H)(|)(C)-undersetunderset(Br)(|)oversetoverset(H)(|)(C)-Br`
This test is not given by alkanes. Hence, it can be used to Distinguish between alkanes and alkenes or alkynes.
(b) Baeyer.s test. If an organic compound decolourises the purple colour of alkaline potassium permanganate solution, then it is unsaturated. (This test is also not given by alkanes).
`gtC=Clt+underset("Purple")(KMnO_(4))+H_(2)O overset(Theta)overset(OH)rarrunderset underset("precipitate")("Brown")(MnO_(2))+ -undersetunderset(OH)(|)overset(|)(C)-undersetunderset(OH)(|)overset(|)(C)-`
The above tests are given by alkenes as well as alkynes, therefore, these cannot be used to distinguish beween them.