Which of the following types of orbital overlapping results in the formation of a $\pi$ bond?

The strongest bond is formed when atomic orbitals undergo:

Considering the $x$-axis as the internuclear axis,which of the following will not form a sigma $(\sigma)$ bond and why?
$(a)$ $1s$ and $1s$
$(b)$ $1s$ and $2p_{x}$
$(c)$ $2p_{y}$ and $2p_{y}$
$(d)$ $1s$ and $2s$

How many $\sigma$ and $\pi$ bonds are present in $CH_3COOH$?

$A$ $\pi$-bond may be formed between two $p_x$-orbitals containing one unpaired electron each when they approach each other appropriately along:

Explain the characteristics of $\pi$ bonds. Or,give the requirements for the formation of $\pi$ bonds and explain the active centers.