d and f Block Elements Part 3

Concept:The reaction between a chloride salt and potassium dichromate in the presence of concentrated sulfuric acid is the chromyl chloride test.Explanation:Sodium chloride and potassium dichromate react with concentrated sulfuric acid upon heating.The balanced chemical equation for this reaction is:$$K_2Cr_2O_7 + 4NaCl + 6H_2SO_4 \rightarrow 2CrO_2Cl_2 + 2KHSO_4 + 4NaHSO_4 + 3H_2O$$The gas evolved is chromyl chloride, $\mathrm{CrO_2Cl_2}$.To find the oxidation state of $\mathrm{Cr}$ in $\mathrm{CrO_2Cl_2}$, assign known oxidation states.Oxygen has an oxidation state of $-2$, and chlorine has $-1$.Let the oxidation state of $\mathrm{Cr}$ be $x$.The net charge on the molecule is zero.The equation is: $x + 2(-2) + 2(-1) = 0$Simplify: $x - 4 - 2 = 0$Thus, $x - 6 = 0$, giving $x = +6$.Answer:The gas is $\mathrm{CrO_2Cl_2}$ and the oxidation state of $\mathrm{Cr}$ is $+6$.Thus, the correct option is C.