Molecule in which the distance between the two adjacent carbon atoms is largest is

Solution :
TIPS/Formulae :
The bond length decreases in the order.
$$\mathop {s{p^3} - s{p^3}}\limits_{{\text{alkane}}} > \mathop {s{p^2} - s{p^2}}\limits_{{\text{alkene}}} > \mathop {sp - sp}\limits_{{\text{alkyne}}} $$
On the basis of the size of the hybrid orbitals, $$sp$$  orbital should form the shortest and $$s{p^3}$$ orbital the longest bond with other atom.