State the differences between sigma $(\sigma)$ and pi $(\pi)$ bonds.

Nodal planes of $\pi$-bond$(s)$ in $CH_2=C=C=CH_2$ are located in

Which of the following overlaps is incorrect (assuming $Z$-axis is the internuclear axis)?
$(A)$ $2p_y + 2p_y \to \pi$-bond formation
$(B)$ $2p_x + 2p_x \to \sigma$-bond formation
$(C)$ $3d_{xy} + 3d_{xy} \to \pi$-bond formation
$(D)$ $2s + 2p_y \to \pi$-bond formation
$(E)$ $3d_{xy} + 3d_{xy} \to \delta$-bond formation
$(F)$ $2p_z + 2p_z \to \sigma$-bond formation

Which type of overlapping results in the formation of a $\pi$ bond?

In which of the following ions is $p\pi - d\pi$ overlap present?

In an acetylene molecule,the bond between the carbon atoms consists of: