One litre of $0.15 \ M \ Na_2SO_3$ aqueous solution is mixed with $500 \ mL$ of $0.2 \ M \ K_2Cr_2O_7$ aqueous solution in acid medium. What is the concentration (in $mol \ L^{-1}$) of unreacted $K_2Cr_2O_7$ in the resultant solution?

Iodine is released when potassium iodide reacts with

Which of the following are non-metal displacement reactions?
$(A)$ $Ca_{(s)} + 2 H_2 O_{(l)} \longrightarrow Ca(OH)_{2(aq)} + H_{2(g)}$
$(B)$ $V_2 O_{5(s)} + 5 Ca_{(s)} \stackrel{\Delta}{\longrightarrow} 2 V_{(s)} + 5 CaO_{(s)}$
$(C)$ $2 Fe_{(s)} + 3 H_2 O_{(g)} \stackrel{\Delta}{\longrightarrow} Fe_2 O_{3(s)} + 3 H_{2(g)}$
$(D)$ $Cr_2 O_{3(s)} + 2 Al_{(s)} \stackrel{\Delta}{\longrightarrow} Al_2 O_{3(s)} + 2 Cr_{(s)}$

In the reaction of sulphur with concentrated sulphuric acid,the oxidised product is $X$ and the reduced product is $Y$. $X$ and $Y$ are respectively:

Which of the following reactions is not feasible?

Which of the following ions decolorizes acidic $KMnO_4$ solution?