A normal solution.
A) Contains one gram equivalent mass of the substance in one liter solution.
B) Contains one gram molecular mass of the substance in one liter solution.
C) Contains one gram equivalent mass of the substance in 100 mL of the solution.
D) Is that whose concentration is known.

Hint: Generally the concentration of all the solutions is supposed to be expressed either in Molarity (M), or Normality (N) or molality (m).
The expression in the unit for the concentration of the solution is going to depend on the quantities of the solute and solvent. Normality is expressed in the number of equivalents per litre.

Complete answer:
> Molarity is defined as the number of moles of a solute present in one liter of a solvent and it is denoted with a symbol ‘M’.
> Normality is defined as the number of gram equivalent weights of a solute present in one liter of the solvent and it is denoted with the symbol ‘N’.
> Molality is defined as the number of moles of solute present in 1 kg of a solvent and it is denoted with a symbol ‘m’.
> Coming to given options, option B, Contains one gram molecular mass of the substance in one liter solution. It is wrong. Because in normality we won’t measure in molecular mass.
> Coming to option C, Contains one gram equivalent mass of the substance in 100 mL of the solution. It is also wrong because generally in normality we have to consider one liter of the solvent not 100 mL.
> Coming to option D, Is that whose concentration is known. It is also wrong because if the concentration is known we cannot call it normality.
> Coming to option A, Contains one gram equivalent mass of the substance in one liter solution. It is correct because it suits the definition of normality.

So, the correct option is A.

Note: Don’t be confused with the words, Molarity, Normality, and Molality. All are not the same but we should use those units to express the amount of the solute which is present in the given solution.
The relationship between molality and molarity is as follows.

\[M=\dfrac{1000md}{1000+m{{M}_{o}}}\]

Here \[{{M}_{o}}\]= Molar mass
d = density
m = molality of the solution
M = molarity of the solution
The relationship between molarity and normality is as follows.
\[N=Molarity\times \dfrac{Molar\text{ }mass}{Equivalent\text{ }mass}\]