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JEE Advanced 2018 Paper 2 · Chemistry · s-Block, p-Block Elements and Hydrogen · medium

Match the thermal decomposition in List-I with the observation in List-II and choose the correct option. List-I P. Strong heating of lead(II) nitrate…

Single correct option

Match the thermal decomposition in List-I with the observation in List-II and choose the correct option.

List-I
P. Strong heating of lead(II) nitrate
Q. Controlled heating of ammonium nitrate at about 500 K500\ \mathrm{K}
R. Heating of ammonium dichromate
S. Heating of sodium azide at about 570 K570\ \mathrm{K}

List-II
1. The solid residue is green
2. The gas evolved turns lime water milky
3. A brown gas is evolved
4. The gaseous product is a nitrogen oxide in which nitrogen has oxidation state +1+1
5. The residue is a metal
  1. A. P→3, Q→1, R→4, S→5
  2. B. P→2, Q→4, R→1, S→5
  3. C. P→3, Q→4, R→1, S→5
  4. D. P→5, Q→4, R→1, S→3
Show answer and solution

Answer: (C) P→3, Q→4, R→1, S→5

Write each balanced equation. P: 2Pb(NO3)2→2PbO+4NO2+O2\mathrm{2Pb(NO_3)_2\rightarrow2PbO+4NO_2+O_2}; the brown gas is NO2\mathrm{NO_2}, so P→3 (the residue PbO is yellow, not green). Q: NH4NO3→N2O+2H2O\mathrm{NH_4NO_3\rightarrow N_2O+2H_2O}; nitrogen in N2O\mathrm{N_2O} is +1+1, so Q→4. R: (NH4)2Cr2O7→N2+Cr2O3+4H2O\mathrm{(NH_4)_2Cr_2O_7\rightarrow N_2+Cr_2O_3+4H_2O}; the solid left is green Cr2O3\mathrm{Cr_2O_3}, so R→1 (the nitrogen evolved is neutral and does not turn lime water milky). S: 2NaN3→2Na+3N2\mathrm{2NaN_3\rightarrow2Na+3N_2}; the residue is metallic sodium, so S→5. No decomposition here releases carbon dioxide, so item 2 is not matched. The unique consistent code is P→3, Q→4, R→1, S→5.
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