Question

# In the metal carbonyls of general formula $$M{(CO)}_{x}$$ if $$M$$ is $$Ni,Fe$$ and $$Cr$$ the value of $$x$$ will be respectively:

A
6, 5, 6
B
4, 5, 6
C
4, 4, 5
D
4, 6, 6

Solution

## The correct option is B 4, 5, 6The EAN rule is as called the 18-Electron Rule. The $$CO$$ ligand donates two electrons to the metal (usually in the 0 oxidation state): $$O≡C:\longrightarrow$$M. Hence ,$$Ni$$ atomic number 28 ($$d^8s^2$$) (10 valence electrons) requires 4 $$CO$$ ligands: $$Ni(CO)_4$$ (nickel tetracarbonyl:) is an extremely poisonous low-boiling liquid. $$Fe$$ atomic number 26 ($$d^6s^2$$) (8 valence electrons) requires 5 $$CO$$ ligands: $$Fe(CO)_5$$ (iron pentacarbonyl) higher boiling straw-coloured liquid, air stable but also poisonous $$Cr$$ atomic number 24($$d^4s^2$$)6 valence electrons (group 6) hence $$Cr(CO)_6$$ (chromium hexacarbonyl) colorless/white air-stable crystals.Hence 4,5,6 is the correct answer.Chemistry

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