Among $\mathrm{PbS}, \mathrm{CuS}, \mathrm{HgS}, \mathrm{MnS}, \mathrm{Ag}_{2} \mathrm{~S}, \mathrm{NiS}, \mathrm{CoS}, \mathrm{Bi}_{2} \mathrm{~S}_{3}$ and $\mathrm{SnS}_{2}$, the total number of BLACK coloured sulfides is

JEE Advanced · 2014 · 25 May 2014 · Paper 1 · Practical and Analytical Chemistry

Among

PbS, CuS, HgS, MnS, Ag_{2} S, NiS, CoS, Bi_{2} S_{3}

and

SnS_{2}

, the total number of BLACK coloured sulfides is

Answer: 6

Solution

The colors of metal sulfides:

$PbS$ — black (galena) ✓
$CuS$ — black (covellite) ✓
$HgS$ — black (metacinnabar, one form; cinnabar is red) ✓
$MnS$ — pink/flesh-colored ✗
$Ag_{2} S$ — black (tarnish on silver) ✓
$NiS$ — black ✓
$CoS$ — black ✓
$Bi_{2} S_{3}$ — black or dark brown ✓ (borderline)
$SnS_{2}$ — yellow/golden ✗

Counting clearly black sulfides: 6 (PbS, CuS, HgS, Ag₂S, NiS, CoS).
If

Bi_{2} S_{3}

is considered black: 7.

Official answer accepts both 6 and 7.

JEE Advanced · 2014 · 25 May 2014 · Paper 1 · Integer answer

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