Which of the following nucleophiles will show minimum reactivity towards $S_N2$ reaction:

$A$ halide $C_5H_{11}Br$ on treatment with alc. $KOH$ gives $2$-pentene only. The halide will be

In which of the following reactions is an anti-Markovnikov product formed?

$CH_3CH_2CH_2OH$ $\xrightarrow{PCl_5} A$ $\xrightarrow{\text{alcoholic } KOH} B$. The final product $B$ is ...... .

Sodium tertiary butoxide on reaction with methyl bromide produces the product $P$.
Sodium methoxide upon reaction with tertiary butyl bromide generates the product $Q$.
The products $P$ and $Q$ are

What are ambident nucleophiles? Explain with an example.