Which of the following substances involve in addition as well as substitution reactions

Acetylene undergoes substitution reactions because the acetylide anion is a powerful nucleophile it may displace halide ions from 1º-alkyl halides to give a more highly substituted alkyne as a product (S_N2 reaction).

Ethylene (Alkene) does not prefer electrophilic substitution reactions due to unstability of intermediate species. 

In this intermediate, sp² carbon is changed to an sp³ carbon with a negative charge, which is less stable.