The nitrogen coming off this reaction is not pure, it carries traces of NO and HNO3 picked up during the NH4Cl plus NaNO2 reaction, so the gas needs to be washed through something that grabs those impurities but leaves N2 completely alone.
N2 is chemically inert under mild conditions, so almost any mild oxidising wash will not touch it, the real test is whether the wash destroys NO and HNO3 without generating a new contaminating gas of its own.
Acidified potassium dichromate is a reliable oxidiser that converts NO into higher, more soluble oxides of nitrogen and mops up the nitric acid traces in the same acidic bath, all while N2 bubbles straight through unreacted.
Checking the alternatives, H2SO4 with SO3 mainly just dries the gas rather than oxidising NO away, H2SO4 with KMnO4 is a much stronger oxidiser that risks side reactions, and HCl with KMnO4 actively generates chlorine gas, which would itself contaminate the nitrogen stream.
So the wash that cleanly removes the impurities is acidified potassium dichromate, and the correct choice is option (2).
Which of the following statements are true?
A. Unlike Ga that has a very high melting point, Cs has a very low melting point.
B. On Pauling scale, the electronegativity values of N and C are not the same.
C. $Ar, K^{+}, Cl^{–}, Ca^{2+} and S^{2–}$ are all isoelectronic species.
D. The correct order of the first ionization enthalpies of Na, Mg, Al, and Si is Si $>$ Al $>$ Mg $>$ Na.
E. The atomic radius of Cs is greater than that of Li and Rb.
Choose the correct answer from the options given below: