The polarity of a chemical bond is determined by the electronegativity difference between the two atoms involved in the bond. Electronegativity is a measure of an atom's ability to attract electrons towards itself in a chemical bond.
In the case of carbon-hydrogen (C-H) bonds, carbon and hydrogen have relatively similar electronegativities. Carbon has an electronegativity value of around 2.55, while hydrogen has an electronegativity value of approximately 2.20 on the Pauling scale. Since the electronegativity difference between carbon and hydrogen is relatively small, the C-H bond is considered non-polar.
However, in the case of 1-alkynes (compounds with a triple bond between two carbon atoms), the situation is slightly different. The carbon atoms participating in the triple bond are sp hybridized, meaning they have a higher electronegativity compared to the sp^3 hybridized carbon atoms in saturated hydrocarbons. The electronegativity difference between the sp hybridized carbon and hydrogen is larger than that between sp^3 hybridized carbon and hydrogen. As a result, the C-H bond in 1-alkynes can exhibit some degree of polarity.
It is important to note that while the C-H bond in 1-alkynes may be considered polar, it is still relatively less polar compared to other types of polar bonds, such as C-O or C-N bonds.