Given a scientific passage and an answer, generate a question for the given answer.

[Q]: Passage: A metallic bond is the force of attraction between a positive metal ion and the valence electrons that surround itboth its own valence electrons and those of other ions of the same metal. The ions and electrons form a lattice-like structure. Only metals, such as the copper pictured in the Figure below , form metallic bonds. Answer: metallic bond
[A]: What is the force of attraction between a positive metal ion and valence electrons?

[Q]: Passage: Benzoic acid crystals in polarized light are pictured above. Benzoic acid is widely used as a food preservative, either as the carboxylic acid or as the sodium benzoate salt. This compound is most effective when added to acidic foods such as fruit juices and soft drinks. The major industrial source of benzoic acid is the partial oxidation of toluene with oxygen. The process is inexpensive and environmentally benign. Answer: benzoic acid
[A]: What type of acid is often used as a preservative for acidic foods such as fruit juices?

[Q]: Passage: Transport of Oxygen in the Blood Although oxygen dissolves in blood, only a small amount of oxygen is transported this way. Only 1.5 percent of oxygen in the blood is dissolved directly into the blood itself. Most oxygen98.5 percentis bound to a protein called hemoglobin and carried to the tissues. Hemoglobin Hemoglobin, or Hb, is a protein molecule found in red blood cells (erythrocytes) made of four subunits: two alpha subunits and two beta subunits (Figure 39.19). Each subunit surrounds a central heme group that contains iron and binds one oxygen molecule, allowing each hemoglobin molecule to bind four oxygen molecules. Molecules with more oxygen bound to the heme groups are brighter red. As a result, oxygenated arterial blood where the Hb is carrying four oxygen molecules is bright red, while venous blood that is deoxygenated is darker red. Answer: hemoglobin
[A]:
Most oxygen in blood is bound to a protein called what, and carried to the tissues?