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

To determine which of the statements regarding nickel and cobalt is correct, let's analyze each statement step by step.

### Step 1: Analyze Statement (a)
**Statement (a): Nickel is a silver white metal.**

- Nickel has an atomic number of 28.
- Its general electronic configuration is [Ar] 3d^8 4s^2.
- Nickel is known for its lustrous, silvery-white appearance.
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