Which halide is not oxidised by $MnO_2$?

Which among the following compounds is $NOT$ a colourless gas?

Which one of the following correctly represents the order of stability of oxides,$X_{2}O$ $(X = \text{halogen})$?

An aqueous solution of a halogen salt of potassium reacts with the same halogen $X_2$ to give $KX_3$,a brown-coloured solution,in which the halogen exists as the $X_3^-$ ion,$X_2$ acts as a Lewis acid,and $X^-$ acts as a Lewis base. The halogen $X$ is:

What is the final chemical form of Gold $(Au)$ when it is dissolved in aqua-regia?

Which of the following is the only existing oxoacid of fluorine?