$1-$chlorobutane on treatment with alcoholic potash forms

$2$-chlorobutane $+ Cl_2 \rightarrow C_4H_8Cl_2$ (isomers)
Total number of optically active isomers shown by $C_4H_8Cl_2$,obtained in the above reaction is......................

The rate of $S_{N}2$ reaction is maximum when the solvent is

Examine the following statements pertaining to an $S_N2$ reaction:
$(1)$ The rate of reaction is independent of the concentration of the nucleophile.
$(2)$ The nucleophile attacks the $C$ atom on the side of the molecule opposite to the group being displaced.
$(3)$ The reaction proceeds with simultaneous bond formation and bond rupture/cleavage.
Amongst the following,which of the above are true?

Identify the product $A$ in the following reaction: $C_2H_5Br + \text{aq. } KOH \rightarrow A + KBr$

An isomer of $C_3H_6Cl_2$ gives acetone on heating with aqueous $KOH$. This isomer is .......