Question

When $Cl_2$ gas reacts with hot and concentrated sodium hydroxide solution, the oxidation number of chlorine changes from

• A. zero to +1 and zero to -5
• B. zero to -1 and zero to +5
• C. zero to -1 and zero to +3
• D. zero to +1 and zero to -3

Answer 1

Answer: (B)

When chlorine gas reacts with hot and
concentrated NaOH solution, it disproportionates
into chloride ($Cl^-$) and chlorate ($C10_3^-$) ions.
In this process, oxidation number of chlorine
changes from 0 to -1 and 0 to +5.
NOTE
In disproportionation reactions, the same element
; undergoes oxidation as well as reduction.