Which of the following $C-H$ bond has the least bond dissociation energy?

Which of the following reactions are not feasible?
$I$. $CH_3CH=CH_2 \xrightarrow{HCl, (C_6H_5CO)_2O_2} CH_3CH_2CH_2Cl$
$II$. $C_6H_6 + CH_3CH_2CH_2Cl \xrightarrow{AlCl_3} C_6H_5CH(CH_3)_2$
$III$. $CH_3CHClCH_2Cl \xrightarrow{KOH, \Delta} CH_3C \equiv CH$
$IV$. $CH_3CH=CHCH_3 \xrightarrow{KMnO_4 / H^+} CH_3COOH$

Provide the bond lengths for hydrogen, ethane, ethene, and ethyne.

Which of the following is the best stereochemical representation for the reaction between $1$-methylcyclohexene and $NBS$ in aqueous dimethyl sulfoxide $(DMSO)$?

The major product of the reaction is:

What is the product $(Q)$ of the following reaction?