In C2H2 three electron pairs are present between two carbon atoms. So three covalent bonds are present between two carbon atoms.
Step-by-step explanation:
Carbon belongs to group 4th A of the periodic table. Each carbon atom contains four electrons in their valence shell. One electron is shared with hydrogen atom to form covalent bond while three electrons remain which combine with other carbon while sharing electrons. In this way three covalent bonds are formed between two carbon atoms.