Question

In NMR the value of alkynyl proton is less than the value of alkenyl proton ,Explain .

Answer 1

Contrasting alkenyl hydrogens, alkynyl hydrogens give rise to shielded hydrogens, or comparatively high field chemical shifts for H-NMR once exposed to an external magnetic field. Infrared spectroscopy is a valuable counterpart to NMR data, and exhibits distinguishing crests for terminal and internal alkynes.

Answer 2

NMR is a research technique that exploits the magnetic properties of certain atomic nuclei. It determines the Physical and Chemical properties of atoms and molecules in which they are contained.
Unlike the Alkenyl hydrogens, Alkynyl hydrogens give rise to shielded hydrogens or relatively high shift from H-NMR when subjeced o external magnetic field. This can be explained by cylindrical pi cloud around Carbon Carbon triple bond. Long range coupling is also observed in alkynes. 
Also Alkenyl hydrogen create external magnetic field that is perpendicular to double bond axis and causes electron in pi bond to rotate in circular path. The circular path of pi bond reinforce the external field where hydrogen are located thus being strongly deshielded and appearing low field in NMR spectrum.