In basic medium, the amount of $Ni^{2+}$ in a solution can be estimated with the dimethylglyoxime reagent. The correct statement$(s)$ about the reaction and the product is (are):

• A
  In an ammoniacal solution, $Ni^{2+}$ salts give a cherry-red precipitate of nickel$(II)$ dimethylglyoximate.
• B
  Two dimethylglyoximate units are bound to one $Ni^{2+}$.
• C
  In the complex, two dimethylglyoximate units are hydrogen bonded to each other.
• D
  Each dimethylglyoximate unit forms a five-membered chelate ring with $Ni^{2+}$.