In which one of the following metal carbonyls, $$\mathrm{CO}$$ forms a bridge between metal atoms?

$$\mathrm{KMnO}_4$$ decomposes on heating at $$513 \mathrm{~K}$$ to form $$\mathrm{O}_2$$ along with

Appearance of blood red colour, on treatment of the sodium fusion extract of an organic compound with $$\mathrm{FeSO}_4$$ in presence of concentrated $$\mathrm{H}_2 \mathrm{SO}_4$$ indicates the presence of element/s

Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R :

Assertion A : Aryl halides cannot be prepared by replacement of hydroxyl group of phenol by halogen atom.

Reason R : Phenols react with halogen acids violently.

In the light of the above statements, choose the most appropriate from the options given below :