When potassium ferrocyanide crystals are heated with concentrated sulphuric acid,the gas evolved is

Sodium thiosulphate $(Na_2S_2O_3 \cdot 5H_2O)$ is used in photography to

The complex formed by carbon monoxide with hemoglobin is called .....

Assign the correct code for Column-$I$ and Column-$II$:

Column-$I$ (Coordination compound)	Column-$II$ (Central metal atom)
$(a)$ Chlorophyll	$(p)$ Rhodium
$(b)$ Blood pigment	$(q)$ Cobalt
$(c)$ Wilkinson catalyst	$(r)$ Calcium
$(d)$ Vitamin $B_{12}$	$(s)$ Iron
	$(t)$ Magnesium

In hemoglobin, the metal ion present is:

Aqueous solution of a metallic nitrate $X$ reacts with $NH_4OH$ to form $Y$,which dissolves in excess $NH_4OH$. The resulting complex is reduced by acetaldehyde to deposit the metal. $X$ and $Y$,respectively,are