Which of the following statements about carbon monoxide are correct?

AIt is an acidic oxide that dissolves in water to give carbonic acid.
BIt reduces $Fe X_{2} O X_{3}$ to iron in the blast furnace.
CIt combines with nickel to form the volatile, tetrahedral $Ni (CO) X_{4}$ .
DIt is poisonous because it binds haemoglobin more strongly than $O X_{2}$ does.

Answer: B, C, D

CO

is a neutral oxide and does not form carbonic acid, so the first statement is false. In the blast furnace

Fe X_{2} O X_{3} + 3 CO 2 Fe + 3 CO X_{2}

. Nickel and

CO

give volatile tetrahedral

Ni (CO) X_{4}

(Mond process).

CO

forms carboxyhaemoglobin, which is more stable than oxyhaemoglobin. Statements 2, 3 and 4 are correct.