JEE Advanced 2025 Paper 2 · Chemistry · s-Block, p-Block Elements and Hydrogen · medium

One mole each of Pb(NO3)2, NaNO3, AgNO3 and Cu(NO3)2 are heated separately and strongly until decomposition is complete (sodium nitrate is taken to…

Numerical answer

One mole each of

\mathrm{Pb(NO_3)_2}

\mathrm{NaNO_3}

\mathrm{AgNO_3}

and

\mathrm{Cu(NO_3)_2}

are heated separately and strongly until decomposition is complete (sodium nitrate is taken to stop at the nitrite stage). The total number of moles of paramagnetic gases evolved from the four samples together is ____. (Ignore dimerisation of

\mathrm{NO_2}

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Answer: 7

The gases that are paramagnetic are

\mathrm{NO_2}

(odd-electron molecule) and

\mathrm{O_2}

(two unpaired electrons); steam and

\mathrm{N_2}

are not formed here.

\mathrm{Pb(NO_3)_2\rightarrow PbO+2NO_2+\tfrac12O_2}

gives

2.5

mol.

\mathrm{NaNO_3\rightarrow NaNO_2+\tfrac12O_2}

gives

0.5

mol (the nitrite is a solid).

\mathrm{AgNO_3\rightarrow Ag+NO_2+\tfrac12O_2}

(the nitrate of an unreactive metal gives the metal) gives

1.5

mol.

\mathrm{Cu(NO_3)_2\rightarrow CuO+2NO_2+\tfrac12O_2}

gives

2.5

mol. The total is

2.5+0.5+1.5+2.5=7

mol.

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