# The percentage of water of crystallisation of a sample of blue vitriol is:$A.34.07\% \\ B.35.07\% \\ C.36.07\% \\ D.37.07\% \\$

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Hint: We must know that the blue vitriol has crystalline copper sulfate having molecular formula. Cupric sulfate, CuSO4, commonly known as blue vitriol, is the most important salt of copper. It usually crystallizes as CuSO4 · 5H2O and has a bright blue colour.

Atomic mass of Copper, Sulphur, oxygen and water is $63.5,{\text{ }}32,{\text{ }}16{\text{ }}and{\text{ }}18$ respectively.
Molecular mass of $CuS{O_4}.5{H_2}O{\text{ }} = {\text{ }}63.5{\text{ }} + {\text{ }}32{\text{ }} + {\text{ }}\left( {4{\text{ }}X{\text{ }}16} \right){\text{ }} + {\text{ }}\left( {5{\text{ }}X{\text{ }}18} \right)$
$\;63.5{\text{ }} + {\text{ }}32{\text{ }} + {\text{ }}64{\text{ }} + {\text{ }}90$
$249.5$
So, the molecular mass of blue vitriol is $249.5g$ and out of which $90g$ is water of crystallization.
$\dfrac{{90}}{{249.5}} \times 100 = 36.07\%$
So, the answer to this question is option C.$36.07\%$.