$A$ mixture of two organic compounds is treated with sodium metal in an ether solvent to produce isobutane. What are these two chloro compounds?

Which of the two stereoisomers of $4-t-$butylcyclohexyl iodide $(^{127}I^-)$ will undergo $S_N2$ substitution with $^{128}I^-$ faster,and why?

In the following pairs of halogen compounds,which compound undergoes faster $S_N1$ reaction?
$(i)$ $2$-chloro-$2$-methylpropane and $3$-chloropentane
(ii) $2$-chloroheptane and $1$-chlorohexane

Among the following rules,the one which is applied in the given reaction is:
$CH_3-CH(Br)-CH_2-CH_3 \xrightarrow{Alc. KOH}$
$I. CH_3-CH=CH-CH_3$ (major product)
$II. CH_2=CH-CH_2-CH_3$ (minor product)

Which among the following is $NOT$ a feature of $S_N2$ mechanism?

Consider the following reactions:
$(a) \; (CH_3)_3CCH(OH)CH_3 \xrightarrow{conc. H_2SO_4} $
$(b) \; (CH_3)_2CHCH(Br)CH_3 \xrightarrow{alc. KOH} $
$(c) \; (CH_3)_2CHCH(Br)CH_3 \xrightarrow{(CH_3)_3CO^{-}K^{+}} $
$(d) \; (CH_3)_2C(OH)CH_2CHO \xrightarrow{\Delta} $
Which of these reaction$(s)$ will not produce Saytzeff product?