Identify ' $A$ ' in the following reaction.

$$ \begin{aligned} &\mathrm{A}+\text { chloromethane } \xrightarrow[\mathrm{AlCl}_3]{\text { Anhydrous }} \text { 2-chlorotoluene }+4 \text {-chlorotoluene } \end{aligned} $$

What is the average rate of reaction when change in concentration of product is 0.05 M in 20 seconds?

Identify the product ' $A$ ' in the following reaction, Anisole $\xrightarrow[398 \mathrm{~K}]{\mathrm{HI}} \mathrm{A}$ + Iodomethane

"Pairing of electrons in the orbitals belonging to the same subshell does not occur unless each orbital belonging to that subshell has got one electron each." This statement is known as