`S_(2) :` Plaster of paris is a hemihydrate of calcium sulphate obtained by heating the gypsum above `393K`.
`S_(2) :` Sodium carbonate is used in water softening.
`S_(4) :` The order of mobilities of the alkali metal ions in aqueous solutions is `Li^(+)gtNa^(+)gtK^(+)gtRb^(+)gtCs^(+)`

The correct order of mobility of the alkali metal ions in aqueous solution is : Rb^+ gtK^+gtNa^+gtLi^+ , Li^+gtNa^+gtK^+gtRb^+ , Na^+gtK^+gtRb^+gtLi^+ , K^+gtRb^+gtNa^+gtLi^+

0.1 M aqueous solution of HClO_4, ZnCl_2 and K_2S are taken , then increasing order of pH of solutions will be :

S_(1) : Mn^(2+) compounds more stable than Fe^(2+) towards oxidation to their +3 state. S_(2) : Titanium and copper both in the first series of transition metals exhibits +1 oxidation state most frequently. S_(3) : Cu^(+) ions is stable in aqueous solutions. S_(4) : The E^(0) value for the Mn^(3+)//Mn^(2+) couple much more positive than that for Cr^(3+)//Cr^(2+) or Fe^(3+)//Fe^(2+) ,