Question

How to distinguish between propyne and but-2-yne

Answer 1

propyne has tripple bond after one carbon atom.
but-2-yne has tripple bond after two carbon atom.

Answer 2

we can distinguish it ny ozoneolysis of propyne and but-2-yne

but-2-yne gives but-2,3-dione

propyne gives prop-1,2-dione