$C{H}_{3}CHO$ and $C_6{H}_{5}C{H}_{2}CHO$ can be distinguished chemically by:

The correct option is B Iodoform test
$C{H}_{3}CHO$ and $C_6{H}_{5}C{H}_{2}CHO$ react with Tollen's reagent, Fehlings solution and Benedict's solution. But $C{H}_{3}CHO$ reacts with $NaOH$ and $I_2$ to give yellow crystals of Iodoform while $C_6{H}_{5}C{H}_{2}CHO$ doesn't react with it. So, iodoform test is used.

$C{H}_{3}CHO+3I_2+4NaOH⟶CH{I}_3+HCOONa+3NaI+3H_{2}O$

$C_6{H}_{5}C{H}_{2}CHO+I_2+4NaOH⟶$ No reaction.