Which of the following halogen oxides is used for the estimation of carbon monoxide in automobile exhaust gases?

An inorganic white crystalline compound $(A)$ has a rock salt structure. $(A)$ on reaction with conc. $H_2SO_4$ and $MnO_2$ evolves a pungent smelling,greenish-yellow gas $(B)$. Compound $(A)$ gives a white precipitate of $(C)$ with $AgNO_3$ solution. Compounds $(A)$,$(B)$,and $(C)$ will be respectively:

Which of the following oxidation states are exhibited by iodine?

What is the product formed when $Au$ reacts with aqua regia?

The correct order of acidic strength of oxy-acids of chlorine is

Which halogen does not show variable oxidation state?