The major product of the following addition reaction is ${\mathrm{H}}_3\mathrm{C}-\mathrm{CH}={\mathrm{CH}}_2\stackrel{{\mathrm{Cl}}_2/{\mathrm{H}}_2\mathrm{O}}{⟶}$

 ${\mathrm{Cl}}^{+}$ reacts as an electrophile, and as a result, the C-O bond develops at the less unstable cation centre. 

Because the secondary carbocation in the given structure is more stable, an OH group is bonded to the second carbon

The reaction is as follows:

${\mathrm{H}}_3\mathrm{C}-\mathrm{CH}={\mathrm{CH}}_2\stackrel{{\mathrm{Cl}}_2/{\mathrm{H}}_2\mathrm{O}}{⟶}$

Hence the correct option is (B).