Question

In which of the following compounds iron has lowest oxidation state?

(a) FeSO₄.(NH₄)₂SO₄.6H₂O

(b) K₄Fe(CN)₆

(c) Fe(CO)₅

(d) Fe₂O

Answer 1

Correct option is (c) Fe(CO)₅

Option (A)

FeSO₄(NH₄)₂SO₄.6H₂O

Let oxidation no. of Fe be x.

And charge on SO₄²⁻ is -2.

charge on NH₄⁺ is +1.

charge on H₂O is 0.

Thus ,

⇒ x + (−2) + 2 × (+1) + (−2) + 6 × 0 = 0

⇒ x − 4 + 2 = 0

∴ x = +2

Option (B)

K₄Fe(CN)₆

Let Oxidation state of Fe be x

Oxidation state of Fe in K₄Fe(CN)₆ will be:

⇒ 4 × (+1) + x + 6 × (−1) = 0

⇒ 4 + x − 6 = 0

∴ x = +2

Option (C)

CO is a neutral molecule thus charge on CO is 0.

Let Oxidation state of Fe be x.

Thus, oxidation state of Fe in Fe(CO)₅ will be :

⇒ x + 5 × 0 = 0

∴ x = 0

Option (D)

Fe₂O

Let Oxidation state of Fe be x

Oxidation state of Fe in Fe₂O will be:

⇒ 2 × x + (−2) = 0

⇒ 2x − 2 = 0

∴ x = +1