Match the salt in List I with the observation on strong heating in List II. List I: (P) CuCO3 (Q) ZnCO3 (R) (NH4)2Cr2O7 (S) Pb(NO3)2 List II: (1) swollen green residue (2) black residue (3) residue yellow when hot and white when cold (4) brown fumes and a residue that is yellow on cooling

JEE Main levelSingle correct optionDifficulty 2 of 3qa008

Match the salt in List I with the observation on strong heating in List II. List I: (P) $CuCO X_{3}$ (Q) $ZnCO X_{3}$ (R) $(NH X_{4}) X_{2} Cr X_{2} O X_{7}$ (S) $Pb (NO X_{3}) X_{2}$ List II: (1) swollen green residue (2) black residue (3) residue yellow when hot and white when cold (4) brown fumes and a residue that is yellow on cooling

CuCO X_{3}

gives black CuO.

ZnCO X_{3}

gives ZnO, yellow hot and white cold.

(NH X_{4}) X_{2} Cr X_{2} O X_{7}

gives swollen green

Cr X_{2} O X_{3}

with

N X_{2}

and steam.

Pb (NO X_{3}) X_{2}

gives brown

NO X_{2}

and PbO, yellow on cooling. The matching is P-2, Q-3, R-1, S-4.