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So I've studied Redox concepts but in the exam we are asked questions like these. How am I supposed to know what the reaction is going to be? How do I go ahead and assume what oxidation state it's going to be and then form the reaction? Do I need to have knowledge about how the reactants interact to answer these questions or is there something only based on redox concepts that I can use to answer this question?

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    $\begingroup$ Think about the products that result from that reaction. Usually, when bubbling chlorine gas over a sodium hydroxide solution, one would get two chlorine based products: chloride and hypochlorite. Here, the conditions are quite different: since the sodium hydroxide solution is both hot and concentrated, it provides a more oxidizing medium. Hence, you might get chloride and a form more oxidized than hypochlorite. $\endgroup$ – TheRelentlessNucleophile Oct 21 at 17:16
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    $\begingroup$ "Do I need to have knowledge about how the reactants interact to answer these questions". Yes, you need to. $\endgroup$ – DatBoi Oct 21 at 17:30
  • $\begingroup$ How would you like a book title "How would I go about naming this book ?" ? BTW screenshots/photos of easy plain text are highly discouraged for multiple reasons. $\endgroup$ – Poutnik Oct 21 at 20:54
  • $\begingroup$ Reaction of chlorine with hot hydroxide is easily available in textbooks or online resources. $\endgroup$ – Poutnik Oct 21 at 20:56
  • $\begingroup$ Yes I understand that. But I wanted to know if students all over the world use anything else - ideas/tricks/mnemonics that'll categorise particular reactions. $\endgroup$ – Om Desai Oct 22 at 19:38

In this case, you have to know that $\ce{Cl2}$ and $\ce{NaOH}$ react at low temperatures according to $$\ce{Cl2 + 2 NaOH -> NaCl + NaClO}$$ and that at high temperature, the hypochlorite $\ce{NaClO}$ gets disproportionated according to $$\ce{3 NaClO -> 2 NaCl + NaClO3}$$ There is no way of predicting it. It must be known. So b) is the good answer.

Note that the preceding reactions may be written with ions instead of sodium compounds.

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