`NH_(3)` solution was added to four semple solution in difference test tube and found the following observation about the precipitate.
a. White ppt which is solution in oxcess of `NH_(3)` solution
b. On heating which is white in cold but yellow on heating
c. The cation present in (b) forms white ppt , with hypo solution which give black ppt on heating
d. The cation present in (c ) forms soluble complex with excess of `NH_(3)` solution
The solution initialy present in (a) `+ H_(2)S` (basic medium) gives ppt , then (a) may have

Options

A. `Zn^(2+)`
B. `Cd^(2+)`
C. `Co^(2+)`
D. `Ni^(2+)`

Answer

a,b