Compound X of the molecular formula $C_4{H}_6$  takes up one equivalent of hydrogen in the presence of Pt to form another compound Y which on oxidative ozonolysis gives only ethanoic acid. The compound X can be?

[Step 1]: ${\text{C}}_{\text{4}}{\text{H}}_{\text{6}}{\text{ + H}}_{\text{2}}\stackrel{\text{Pt}}{\to }{\text{ C}}_{\text{4}}{\text{H}}_{\text{8}}\stackrel{\text{Ozonolysis}}{\to }{\text{ 2 CH}}_{\text{3}}\text{COOH}$

          to get only ethanoic acid the alkene which undergoes ozonolysis must be 2–butene from the above reaction

          [Step 2]: $C{H}_2=CH-CH=C{H}_2{\text{ + H}}_{\text{2}}\stackrel{\text{Pt}}{\to }C{H}_3-CH=CH-C{H}_3\stackrel{\text{Ozonolysis}}{\to }{\text{ 2 CH}}_{\text{3}}\text{COOH}$

          But–1,3–diene on mono hydrogenation will undergo 1,4–addition can form 2–butene, further ozonolysis of 2–butene will give only ethanoic acid 

          [Step 3]: $C{H}_3-C\equiv C-C{H}_3{\text{+ H}}_{\text{2}}\stackrel{\text{Pt}}{\to }C{H}_3-CH=CH-C{H}_3\stackrel{\text{Ozonolysis}}{\to }{\text{ 2 CH}}_{\text{3}}\text{COOH}$

          But–2–yne on mono hydrogenation will give 2–butene, further ozonolysis of 2–butene will give only ethanoic acid 

          [Step 4]: $C{H}_2=C=CH-C{H}_3{\text{ + H}}_{\text{2}}\stackrel{\text{Pt}}{\to }C{H}_3-CH=CH-C{H}_3\stackrel{\text{Ozonolysis}}{\to }{\text{ 2 CH}}_{\text{3}}\text{COOH}$

          But–1,2–diene on mono hydrogenation will undergo 1,2–addition can form 2–butene, further ozonolysis of 2–butene will give only ethanoic acid