What will happen ? (Also write the chemical equations).
(a) When a filter paper moistened with potassium iodate and starch solution is brought in contact with sulphur dioxide gas.
(b) When `H_(2)S` gas is made to react with sodium tetrahydroxidoplumbate (II) solution.
(c ) When sulphite reacts with dilute `H_(2)SO_(4)` in presence of zinc

Explanation

(a) Blue colouration develops due to the formation of iodine gas.
`5 SO_(2)+2lO_(3)^(-)+4 H_(2)O to l_(2)+5 SO_(4)^(2-) +2H^(+)`
`l_(2) + "Starch" to ` Blue (starch iodine adsorption complex)
(b) Black precipitate is formed owing to the formation of PbS.
`[Pb(OH)_(4)]|^(2-) + H_(2)S to PbS darr + 2OH^(-) +2 H_(2)O`
(c ) `SO_(3)^(2-) +3 Zn + 8 H^(+) to H_(2)S +3 Zn^(2+) +3 H_(2)O`