!!CaOCl_(2) + H_(2)Orarr Ca(OH)_(2)+X!!
!!X + CH_(3)CHO rarrY!!
!!Y + Ca(OH)_(2)rarr CHCl_(3)!!
What is 'Y'?
Source: Eamcet 2007
In the first reaction, X is !!Cl_(2)!!. In second reaction chlorine is reacting with acetaldehyde, this is the halogenation reaction of carbonyl compounds in which all the !!alpha!! hydrogens of the aldehyde will get substituted by chlorine molecules thus giving !!C Cl_(3)CHO!! . This will react with calcium hydroxide to produce chloroform.