Distinction between pairs of compounds
Ethanol `(CH_(3)CH_(2)OH)` and Phenol `(C_(6)H_(5)OH)`

Explanation

These can be distinguished by the iodoform test.
Ethanol due to the presence of the grouping `CH_(3)CHOH` - gives yellow ppt. of iodoform on warming with NaOI, i.e., NaOH and `I_(2)`.
`underset("Ethanol")(CH_(3)CH_(2)OH)+NaOIunderset("Ethanal")(rarrCH_(3)CHO)+NaI+H_(2)O`
`CH_(3)CHO+3NaOIrarrunderset("Iodoform")(CHI_(3))darr+undersetunderset("(Yellow ppt.)")("Sod. formate")(HCOONa)+2NaOH`
On the other hand, 1-propanol does not contain the grouping
`CH_(3)CHOH` - and hence it does not give iodoform test on treatment with NaOH and `I_(2)(NaOI)`.