${C_3}{H_7}OH\,\xrightarrow{{{H_2}S{O_4}}}X\,\xrightarrow{{B{r_2}}}\,Y\xrightarrow{{KOH}}Z$
$1. {{H}_{3}}C-\overset{+}{\mathop{O}}\,{{H}_{2}}\to CH_{3}^{+}+{{H}_{2}}O$
$2. (CH_3)_3 C - \overset{+}{\mathop{O}}\,{{H}_{2}} \to (CH_3)_3 C^+ + H_2O$
$3. (CH_3 )_2CH - \overset{+}{\mathop{O}}\,{{H}_{2}} \to (CH_3)_2 CH^+ + H_2O$