Arrange the following compounds in decreasing order of acidity.
`H_(2)O, ROH, HC -= CH`

Explanation

A stronger acid displaces a weaker acid from its salt. When RONa is treated with `H_(2)O`, it forms ROH, so water is a stronger acid than ROH.
`underset("Stronger acid")(HOH)+RONa rarr NaOH + underset("Weaker acid")(ROH)`
Similary, when sodium ethynide is treated with water and alcohol, then acetylene is obtained.
`underset("Stronger acid")(HOH)+CH-=CNa rarr underset("Weak acid")(HC -= CH)+NaOH`
`underset("Stronger acid")(ROH)+HC-=CNa rarr underset("Weak acid")(HC -= CH)+RONa`
Thus, water and aclohol are strongest acid than ethyne and the decreasing order of acidity of given compounds are
`HOH gt ROH gt HC -= CH`