The given reaction is called _______
\(\ce{CaO + H2O -> Ca(OH)2}\)
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Combination Reaction
A combination reaction is one in which two or more substances join to form a single product. Here calcium oxide (quicklime) and water join to give one product, calcium hydroxide (slaked lime), with the release of a lot of heat. This is the reaction that takes place when lime is slaked for whitewashing.
Why the other options are incorrect
Option (1) Dissociation Reaction — Incorrect. In dissociation one substance breaks up into smaller parts, the opposite of what happens here.
Option (2) Substitution Reaction — Incorrect. In substitution one atom or group takes the place of another, so two products form, not one.
Option (4) Addition Reaction — Incorrect. This term is used in organic chemistry for atoms adding across a double or triple bond, as in the hydrogenation of oils.