Noble metals,like gold and platinum,are soluble in which of the following mixtures?

Yellow color of chlorine water fades because of:

The colour of the $X_2$ molecules of group $17$ elements changes gradually from yellow to violet down the group. This is due to
[$A$] the physical state of $X_2$ at room temperature changes from gas to solid down the group
[$B$] decrease in $HOMO-LUMO$ gap down the group
[$C$] decrease in $\pi^*-\sigma^*$ gap down the group
[$D$] decrease in ionization energy down the group

When a mixture of solid $NaCl$ and solid $K_2Cr_2O_7$ is heated with concentrated $H_2SO_4$,orange-red vapours are evolved. These vapours are of which compound?

The correct statement$(s)$ regarding $(i) HClO$,$(ii) HClO_2$,$(iii) HClO_3$,and $(iv) HClO_4$ is(are):
$(A)$ The number of $Cl=O$ bonds in $(ii)$ and $(iii)$ together is two.
$(B)$ The number of lone pairs of electrons on $Cl$ in $(ii)$ and $(iii)$ together is three.
$(C)$ The hybridization of $Cl$ in $(iv)$ is $sp^3$.
$(D)$ Amongst $(i)$ to $(iv)$,the strongest acid is $(i)$.

$HBr$ and $HI$ reduce sulphuric acid,$HCl$ can reduce $KMnO_4$ and $HF$ can reduce: