Which of the following is least reactive towards nucleophilic substitution reaction?

The major product of the reaction is:

The hybridization state of carbon atoms in the product formed by the reaction of ethyl chloride with aqueous potassium hydroxide is

Explain the order of reactivity of $1^o$,$2^o$,and $3^o$ halides towards the $S_N2$ reaction.

What is the major product of the following reaction?
$CH_2=CH-CH_2-CH(Br)-CH_3 + KOH \xrightarrow[\text{heat}]{\text{alcohol}} \dots$

Which of the following alkyl halides gives only one product (excluding stereoisomers) when undergoing an $E_2$ reaction? $(E_2 = \text{elimination bimolecular})$