Question

What is regioselectivity$?$

Answer 1

First we know selectivity is expressed by ratios of rate constants of the competing reactions, or by the logarithms of these ratios. Then mention the types of selectivity. After that write what is regioselectivity. Give some examples.

Complete answer:
Selectivity is the discrimination shown by a reagent in competitive attack on two or more substrates or on two or more positions in the same substrate.
There are three types of selectivity possible for any reaction:
Chemoselectivity is deciding which group reacts.
Regioselectivity is where the reaction takes place in that group.
Stereoselectivity is how the group reacts with respect to the stereochemistry of the product.
Regioselectivity is the preference of chemical bonding or breaking in one direction over all other possible directions. The description of a reaction's regioselectivity (or the absence of regioselectivity) is called the reaction's regiochemistry.
Regioselectivity occurs in chemical reactions where one reaction site is preferred over another. For example, the addition of an asymmetric reagent (such as $H - Cl$) to an asymmetric alkene may yield two different products. The reaction is regioselective if one of the two products is preferred over the other. Markovnikov additions are common examples of regioselective reactions.

Note:
Note that a term Chemo-selectivity, used in organic chemistry to describe reactivity of one functional group in the presence of other groups. A term Stereoselectivity used in organic chemistry to describe the distribution of isomers in reaction products.