On heating a mixture of common salt and $$K_{2}Cr_{2}O_{7}$$ in equal amount along with concentrated $$H_{2}SO_{4}$$ in a test tube, a gas is evolved. Formula of the gas evolved and oxidation State of the central metal atom in the gas respectively are:

We need to identify the gas evolved when a mixture of common salt (NaCl) and potassium dichromate ($$K_2Cr_2O_7$$) is heated with concentrated $$H_2SO_4$$, and find the oxidation state of the central metal atom.

This reaction corresponds to the chromyl chloride test, a well-known reaction used for the detection of chloride ions. The balanced equation is:

$$ K_2Cr_2O_7 + 4NaCl + 6H_2SO_4 \rightarrow 2KHSO_4 + 4NaHSO_4 + 2CrO_2Cl_2\uparrow + 3H_2O $$

The gas evolved is chromyl chloride, $$CrO_2Cl_2$$. It is a dark red (reddish-brown) gas with an acrid smell.

In $$CrO_2Cl_2$$ each oxygen has oxidation state = $$-2$$ and each chlorine has oxidation state = $$-1$$. Let the oxidation state of Cr = $$x$$, then $$ x + 2(-2) + 2(-1) = 0 $$ $$ x - 4 - 2 = 0 $$ $$ x = +6 $$.

Note that the formula is $$CrO_2Cl_2$$ (one Cr atom), not $$Cr_2O_2Cl_2$$ (which would be a dimer). The chromyl chloride molecule has a tetrahedral structure around Cr, with two Cr=O double bonds and two Cr-Cl bonds.

The correct answer is Option (4): $$CrO_2Cl_2$$ and +6.