Which of the following compounds will undergo $S_{N^1}$ reaction most easily?

Increasing the concentration of an electrophile (substrate) in a typical $S_N2$ reaction by a factor of $3$ and the concentration of the nucleophile by a factor of $3$ will change the reaction rate to

Among the following,the compounds which can undergo an $S_{N}1$ reaction in an aqueous solution are:

Reaction of $(R)-2$-butanol with $p$-toluenesulphonyl chloride in pyridine followed by $LiBr$ gives:

Why is chloroform stored in dark-coloured bottles?

An 'Assertion' $(A)$ and a 'Reason' $(R)$ are given below. Choose the correct answer from the following options.
Assertion $(A)$: Vinyl halides do not undergo nucleophilic substitution easily.
Reason $(R)$: Even though the intermediate carbocation is stabilized by loosely held $p-$ electrons,the cleavage is difficult because of strong bonding.