Which of the following statements is correct?
(a). Nickel is a silver white metal.
(b). Nickel dimethylglyoxime is square planer.
(c). Among complexes of cobalt the most stable are those of `Co^(2+)`,
(d). Among simple compounds of cobalt the most stable are those of `CO^(2+)`.

Explanation

a,b,d
`Co^(2+)` state is stable in simple compounds of cobalt while the `+3` state is more stable in complexes.