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Question: The products obtained when chlorine gas reacts with cold and dilute aqueous \({\rm{NaOH}}\) are: A...

The products obtained when chlorine gas reacts with cold and dilute aqueous NaOH{\rm{NaOH}} are:
A. ClO−  and ClO3−{\rm{Cl}}{{\rm{O}}^ - }\;{\rm{and \,ClO}}_3^ -
B. Cl−  and ClO−{\rm{C}}{{\rm{l}}^ - }\;{\rm{and \,Cl}}{{\rm{O}}^ - }
C. Cl−  and ClO2−{\rm{C}}{{\rm{l}}^ - }\;{\rm{and \,ClO}}_2^ -
D. ClO−  and ClO3−{\rm{Cl}}{{\rm{O}}^ - }\;{\rm{and \,ClO}}_3^ -

Explanation

Solution

We have known halogens to have an oxidation state of −1 - 1 but it has been observed that chlorine, bromine and iodine can exist with other oxidation states as well including +1,+3,+5 + 1, + 3, + 5 and +7 + 7 where these electronegative elements are bound to more electronegative halogen (fluorine) or oxygen. On the similar lines, chlorine can form different oxides including Cl2O,ClO2,Cl2O6,Cl2O7{\rm{C}}{{\rm{l}}_2}{\rm{O}},{\rm{Cl}}{{\rm{O}}_2},{\rm{C}}{{\rm{l}}_2}{{\rm{O}}_6},{\rm{C}}{{\rm{l}}_2}{{\rm{O}}_7} etc.

Complete answer:
Chlorine can also react with alkalis to give a mixture of products in which chlorine is present in different oxidation states. The nature of these products depends upon whether we have used hot and concentrated alkali or cold and dilute alkali. Let’s have a look at the reactions that will take place in both the cases.
If we use hot and concentrated alkali to react with chlorine, we will get chloride and chlorate. We can write the chemical equation by taking sodium hydroxide as alkali reacting with chlorine as follows:
3Cl2+6NaOH→5NaCl+NaClO3+3H2O{\rm{3C}}{{\rm{l}}_2} + 6{\rm{NaOH}} \to {\rm{5NaCl}} + {\rm{NaCl}}{{\rm{O}}_{\rm{3}}} + {\rm{3}}{{\rm{H}}_{\rm{2}}}{\rm{O}}
On the other hand, if we use cold and dilute alkali to react with chlorine, we will get chloride and hypochlorite. We can write the chemical equation by taking sodium hydroxide as alkali reacting with chlorine as follows:
Cl2+2NaOH→NaCl+NaOCl+H2O{\rm{C}}{{\rm{l}}_2} + 2{\rm{NaOH}} \to {\rm{NaCl}} + {\rm{NaOCl}} + {{\rm{H}}_{\rm{2}}}{\rm{O}}
Now, in this case, we can see that we have chloride that has chemical formula as Cl−{\rm{C}}{{\rm{l}}^ - } and hypochlorite that has chemical formula as ClO−{\rm{Cl}}{{\rm{O}}^ - }.

**Hence, the correct option is B.

Note: **
In anions such as hypochlorite, chlorite, hypochlorite or chlorate, we will have the negative charge on oxygen not chlorine as oxygen is more electronegative than chlorine that is why chlorine is present with positive oxidation state in these anions.