Redox

Cl2 + 2NaOH → NaCl + NaOCl + H2O

The O.N. of Cl in Cl2 is 0.
The O.N. of Cl in NaCl is -1.
The O.N. of Cl in NaOCl is +1.
Is it a redox and is chlorine responsible in both oxidizing agent and reducing agent?


Yes, it is a redox reaction and chlorine is responsible in both oxidizing agent and reducing agent.

Cl2 acts as an oxidizing agent (undergoes reduction):
Cl2 + 2e¯ → 2Cl¯ …… (1)

Cl2 also acts as a reducing agent (undergoes oxidizing):
Cl2 + 4OH¯ → 2OCl¯ + 2H2O + 2e¯ …… (2)

(1) + (2):
2Cl2 + 4OH¯ → 2Cl¯ + 2OCl¯ + 2H2O
i.e., Cl2 + 2OH¯ → Cl¯ + OCl¯ + H2O

Adding 2Na⁺ to the both side of the equation, it becomes
Cl2 + 2NaOH → NaCl + NaOCl + H2O

The reaction in which the same kind of atom acting as both the oxidizing agent and the reducing agent is known as "disproportionation".

i've to add that "disproportionation" refers to a reaction that an element with same oxidation state undergoes reduction and oxidation simultaneously.
example is reaction of chlorine and sodium hydroxide.

2010-10-17 18:15:23 補充：
when species of element of different O.N. comes to equal, it's called "coproportionation".
example is addition of hydrochloric acid to chlorine bleach. hypochlorite (+I) turns to chlorine (0), chloride (-I) turns to chlorine (0).