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Which of the following might turn $\ce{NaNO2}$ into $\ce{N2}$?

A. $\ce{NaCl}$ B. $\ce{NH4Cl}$ C. $\ce{HNO3}$ D. $\ce{H2SO4}$

The answer is B and we have $$\ce{NH4Cl + NaNO2 = NaCl + 2H2O + N2↑}.\tag1$$

How can we solve this multiple choice question without knowing $(1)$?

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    $\begingroup$ To get elemental nitrogen for Sodium Nitrite you need to reduce the nitrite. Only B contains a reasonable reducing agent, the ammonium ion. So it must be B. $\endgroup$
    – Ian Bush
    Commented Nov 11, 2023 at 7:24
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    $\begingroup$ The ability to answer questions requires knowledge of facts or principles leading to them. That is valid in chemistry, in science and all human activities. $\endgroup$
    – Poutnik
    Commented Nov 11, 2023 at 7:29
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    $\begingroup$ You can't. Or rather, you can conclude that (B) is the only compound here containing N in negative oxidation state, which may lead to some beneficial consequences... but that very way of thinking only develops when you know a good deal of chemistry, and in particular a great many reactions, most likely including (1). $\endgroup$ Commented Nov 11, 2023 at 8:04

1 Answer 1

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To get N2 from NaNO2, NaNO2 must be reduced right, So we need a reducing agent which oxidizes itself and would reduce NaNO2

Now look at the options

Let's see HNO3, the oxidation state of Nitrogen is already $+5$ and since $+5$ is the highest oxidation state, there is no chance of HNO3 to get oxidized further. So it cannot reduce NaNO2.

The same analogy goes with H2SO4 ( S is already in its highest oxidation state $+6$ ), Also Na+ cannot get oxidised further also.

NH4Cl can get oxidised as N's oxidation state is in $-3$, This could be a good way to guess the answer for a multiple choice question, You will also not able to guess between two reducing agents, you should know the reaction anyways.

But as Poutnik did state in comments - "The ability to answer questions requires knowledge of facts or principles leading to them. That is valid in chemistry, in science and all human activities", You would need the knowledge of the reaction to answer such questions.

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    $\begingroup$ Wonderful idea! The problem was probably intended to examine knowledge about redox, instead of any particular reaction. $\endgroup$
    – youthdoo
    Commented Nov 11, 2023 at 12:15

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