A bond between two sugar molecules is formed by which of the following types of reactions?

oxidation-reduction

condensation

single-replacement

double-replacement

ROH + HOR' ==>ROR' + H2O

Condensation.
http://en.wikipedia.org/wiki/Sucrose

The bond between two sugar molecules is formed by a type of reaction called condensation.

To understand why, let's break it down:

1. Oxidation-reduction reactions involve the transfer of electrons between atoms or molecules. This type of reaction usually results in the formation or breaking of bonds with changes in oxidation states.

2. Single-replacement reactions occur when one element replaces another element in a compound. They involve the transfer of atoms or ions.

3. Double-replacement reactions occur when two compounds exchange ions to form two new compounds.

4. Condensation reactions, on the other hand, involve the combination of two molecules to form a larger molecule, which usually involves the removal of a small molecule, such as water. This type of reaction is typical in the formation of many biological macromolecules, including the bond between two sugar molecules. In this case, the bond forms between the hydroxyl groups (-OH) of the sugar molecules, while a water molecule is eliminated.

Therefore, the correct answer is "condensation."