${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\stackrel{{\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7/{\mathrm{H}}^{+}}{\to }\left(\mathrm{X}\right)\stackrel{\left(\mathrm{O}\right)}{⟶}\left(\mathrm{Y}\right)$ ; What is ‘Y’ ?

As Potassium Dichromate is a powerful oxidising agent, the alcohol will be oxidised, first to the aldehyde (acetaldehyde in this case) and then to the carboxylic acid (acetic acid).

${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\stackrel{{\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7/{\mathrm{H}}^{+}}{\to } {\mathrm{CH}}_3\mathrm{CHO}\stackrel{\left(\mathrm{O}\right)}{⟶} {\mathrm{CH}}_3\mathrm{COOH}$