A solution of a colourless salt when acidified with dil. HCl , slowly turns milky with a pale yellow tint. When `AgNO_(3)` solution is added to the solution of the salt, white ppt. slowly changing to yellow, orange, brown and finaly to black is obtained. the anion present in the salt is
A. `Br^(-)`
B. `SO_(3)^(2-)`
C. `S_(2)O_(3)^(2-)`
D. `I^(-)`