Answer

A-Q ; B-PS ; C-PR; D-P

Explanation

Isobutane-(Q) Constituent of LPG
But-2-ene-(P.S) Decolourises `Br2// C CI_4`,Gives only ethanol on reductive ozonolysis
But-1-yne-P,R- Decolourises, Evolves With But-2-yne-P- Decolourises