Question

why is bond formed between carbon and carbon weak in acetylene​

Answer 1

Answer:

covalent bond is the answer

Answer 2

Answer:

The carbon atom doesn't have enough unpaired electrons to form four bonds (1 to the hydrogen and three to the other carbon), so it needs to promote one of the 2s2 pair into the empty 2pz orbital. This is exactly the same as happens whenever carbon forms bonds - whatever else it ends up joined to.

Explanation: