Option B is correct.
The reaction of an acid and a base is called a neutralization reaction. The general reaction between an acid and a base is:
acid + base → water + salt

In chemistry, the term salt is generally used to define any ionic compound either soluble or insoluble that is formed from a reaction between an acid and a base not just the table salt. In the neutralization reaction between HCl(aq) and KOH(aq) the result is:
HCl(aq) + KOH(aq) → H2O(l) + KCl(aq)

Acid Base Water Salt

The salt generated here is KCl. By counting the number of atoms of each element, we find that only one water molecule is formed as a product and the chemical equation is balanced. All other options above are wrong.

Option B - It tells when the equivalence point is obtained, this is the purpose of an indicator in the solution with the unknown concentration.

An indicator is a substance that changes color in response to a chemical change. An acid–base indicator. It detects hydronium ions (H3O+) or hydrogen ions (H+) in the Arrhenius model.
Option A - is not the main function of an indicator.
Option C - is also not the main function of an indicator.

HCl and H2O.

H2O is amphoteric so it can act as both a Bronsted acid or base at neutral conditions.

NH3 is a Bronsted-Lowry base at pH = 9 and below. It acts as an Bronsted-Lowry acid at pH's above 9. Since the question does not specify conditions, we should assume this to be at a neutral condition (pH = 7) which would make NH3 a base.