The evolution of a red-brown gas on heating a salt with $K_{2}C{r}_2{O}_7$ and concentrated $H_{2}S{O}_4$ can arise from: 

A chloride will given $Cr{O}_{2}C{l}_2,$ bromide will give $B{r}_2,$ and nitrate and nitrite will give $N{O}_2.$ All these gases are red-brown.