Answer
A. Reactions involving replacement of one atom or group of atoms by another.
B. In an addition reaction, formation of a single product from two reactant molecules takes place.
C. In an elimination reaction, removal of a small molecule from a larger molecule takes place.
Work Step by Step
A) Example:
$CH_{3}CH_{2}OH +HBr$ -> $CH_{3}CH_{2}Br + H_{2}O$
In this reaction halogen replaces hydroxyl group on the alcohol. This is a substitution reaction since replacement of one atom or group of atoms by another takes place.
B) Example:
Molecules containing double or triple bonds undergo addition reactions. Example, alkenes, alkynes etc.
Eg. $CH_{3}CH_{2}CH=CH_{2} +Br_{2}$ -> $CH_{3}CH_{2}CHBrCH_{2}Br$
Two molecules joins together to form a single product.
C) Example:
In the presence of concentrated acid, alcohols react and water is eliminated Resulting in the formation of an alkene. This is an example of elimination reaction since a small molecule is eliminated from a larger one.
