Ethyl orthoformate is formed by heating which of the following compounds with sodium ethoxide?

Increasing order of reactivity of the following compounds for $S_N1$ substitution is:
$(a)$ $(CH_3)_2CH-CH_2Cl$
$(b)$ $CH_3CH_2Cl$
$(c)$ $CH_3O-C_6H_4-CH_2Cl$
$(d)$ $C_6H_5-CH_2Cl$

When chloroform is exposed to air and sunlight,it gives

Identify the reagent used in the following conversion:
$CH_3CH_2Cl \xrightarrow{A} CH_3CH_2NO_2$ (Nitroethane)

In the dehydrohalogenation of $2$-bromobutane,which conformation leads to the formation of $cis$-but-$2$-ene?

Write about the $\beta$-elimination reactions of haloalkane compounds.