Question

Which of the following statements is not applicable to Lassaigne's test?

• A. The extra elements (N, S and halogens) are tested as their inorganic salts.
• B. During fusion of the organic compound iwth sodium, $N{a}_{2}S,NaCN$ and $NaX$ are formed.
• C. It can even be used for the detection of hydrogen in the organic compound.
• D. It is possible to differentiate between the different halogens.

Answer 1

The correct option is C It can even be used for the detection of hydrogen in the organic compound.

Lassaignes test
$Na+C+N\stackrel{a}{\to }NaCN$
$2Na+S\to N{a}_{2}S$
$Na+X\to N{a}_{2}S$
Option (a) is correct
when sulphur is also present
$Na+C+N+S\to NaCNS$
$3CN{S}^{-}+F{e}^{3+}\to \underset{\text{Blood red}}{Fe(CNS{)}_3}$
$NaSCN+2Na\to NaCN+N{a}_{2}S$
option (b) is correct
For testing halogens
$AsN{O}_3+NaX\to AgX\downarrow +NaN{O}_3$
when X = Cl
$AgCl$ (white ppt) soluble in $N{H}_{4}OH$
When X = I
$AgI$ (Dark-yellow ppt) is soluble in $N{H}_{4}OH$
option (d) is correct.
It can't be used for the detection of hydrogen in the organic compounds. Method for the detection of C and H is known as Liebig's Method

So the answer is the option (c).