Which of the following is an isomer of diethyl ether $(C_4H_{10}O)$?

An organic compound $A$ reacts with sodium metal and forms $B.$ On heating with conc. $H_2SO_4,$ $A$ gives diethyl ether. $A$ and $B$ are

Identify product $B$ in the following reaction sequence:
$(CH_3)_2C=C(CH_3)_2$ $\xrightarrow{X_2, H_2O} A$ $\xrightarrow{OH^{-}} B$

The solubility of anhydrous $AlCl_3$ and hydrous $AlCl_3$ in diethyl ether are $S_1$ and $S_2$ respectively. Then:

Explain the following with an example.
$(i)$ Kolbe's reaction.
$(ii)$ Reimer-Tiemann reaction.
$(iii)$ Williamson ether synthesis.
$(iv)$ Unsymmetrical ether.

Scheme $1$ and $2$ describe the conversion of $P$ to $Q$ and $R$ to $S$,respectively. Scheme $3$ describes the synthesis of $T$ from $Q$ and $S$. The total number of $Br$ atoms in a molecule of $T$ is. . . . . . . .