It means \(-CHO\) group is present.
It means only one \(-CHO\) group is present.
\({C_2}{H_5}OH + C{l_2} \to C{H_3}CHO + 2HCl\)
\(C{H_3}CHO + 3C{l_2} \to \mathop {CC{l_3}CHO}\limits_{{\rm{Chloral}}} + 3HCl\)

$[Figure]$ $\xrightarrow[{Heat}]{{NaOC{H_3}\left( {1\,eq.} \right)}}$
