How will you prove:
acidic character of acetylene.

Explanation

When acetylene is added to water and shaken ,the resulting solution does turn blue litmus red. The following reactions in which the H-atoms of acetylene are replaced by metal atom prove the acidic character of acetylene.
(a) Acetylene `(HC-=CH)` reacts with sodium in two steps to form monosodium acetylide `(HC-=CNa)` and disodium acetylide `(NaC-=CNa)` respectively and in each case, `H_2` is evolved.
`2[HC-=CH]+2Naoverset(Delta)to2[HC-=CNa]+H_2uarr`
`2[HC-=CNa]+2Naoverset(Delta)to2NaC-=CNa+H_2uarr`
(b) When acetylene gas is passed through ammoniacal `Cu_2Cl_2 or AgNO_3` solution , metallic acetylide is precipitated in each case.
`C_2H_2+Cu_2Cl_2+2NH_4OHtounderset((red))(Cu_2C_2darr)+2NH_4Cl+2H_2O`
`C_2H_2+2AgNO_3+2NH_4OHtounderset((White))(Ag_2C_2darr)+2NH_4NO_3+2H_2O`