dear sir in the video on oxidation number in the rapid fire round, why do you say the oxidation number of carbon is zero in ch2cl2.

Chlorine is the most electronegative element and so it gets its standard charge of -1 for each Chlorine atom.

both Hydrogen atoms are given an oxidation number of +1.

In order to tally to zero, we MUST assign Carbon the oxidation number of 0. Therefore we can confidently state that after following the oxidation number rules, Carbon has an oxidation number of 0 in this compound.