Which one is most reactive towards S_N1 reaction?

1. $C_6{H}_{5}CH\left(C_6{H}_5\right)Br$

2. $C_6{H}_{5}CH\left(C{H}_3\right)Br$

3. $C_6{H}_{5}C\left(C{H}_3\right)\left(C_6{H}_5\right)Br$

4. $C_6{H}_{5}C{H}_{2}Br$

In a S_N2 substitution reaction of the type 
\(\mathrm{R}-\mathrm{Br}+\mathrm{Cl}^{-} \xrightarrow{\mathrm{DMF}} \mathrm{R}-\mathrm{Cl}+\mathrm{Br}^{-}\)

one of the following that has the highest relative rate is:
 

1.	\(\mathrm{CH}_3-\mathrm{CH}_2-\mathrm{CH}_2 \mathrm{Br}\)	2.
3.		4.	\(\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{Br}\)