(a) Fluorine cannot be prepared from fluorides by chemical oxidation. Why?
(b) Anhydrous `HCl` is bad conductor of electricity while aqueous `HCl` is a good conductor. Give reason.
(c ) Fresh iodine stain can be removed by washing with hypo solution. Explain.

Explanation

(a) The standard reduction potential of fluorine is maximum. Thus, it cannot be oxidised by any other reagent. Fluoride ion is very stable due to small size and high electronegativity of fluorine atom. Thus, fluorine cannot be prepared from fluorides by chemical oxidation.
(b) In anhydrous state, `HCl` is a covalent molecule, hence bad conductor of electricity. Whereas , in aqueous state, `HCl` ionises and acts as good conductor.
`HCl+H_(2)O rarr H_(3)O^(o+)+Cl^(Ө)`
(c ) Hypo solution i.e. sodium thiosulphate, `Na_(2)S_(2)O_(3).5H_(2)O` reacts with iodine to form water soluble colourless sodium tetrathionate and sodium iodide.
`{:(2Na_(2)S_(2)O_(3)+I_(2)to2NaI+Na_(2)S_(4)O_(6)),(or 2S_(2)O_(3)^(2-)toS_(4)O_(6)^(2-)+2e^(Ө)),(I_(2)+2e^(Ө)to2I^(Ө)),(ulbar(2S_(2)O_(3)^(2-)+I_(2)toS_(4)O_(6)^(2-)+2I^(Ө))):}`