Which of the following alkyl halides is most reactive towards the $E_2$ mechanism?

Which is correct for the above reaction $:-$

Which one of the following forms propane nitrile as the major product?

Given below are two statements:
Statement $I$: $(CH_3)_3C-CH_2-Cl$ will undergo $S_N1$ reaction even though it is a primary halide.
Statement $II$: It will not undergo $S_N2$ reaction very easily even though it is a primary halide.
In the light of the above statements,choose the most appropriate answer from the options given below:

On what factors does the rate (reactivity) of the $S_{N}1$ reaction depend? Explain with suitable examples.

Consider the following bromides.
The correct order of $S_N1$ reactivity is