Volume of a regular circular cylinder is ________ cubic units.
\[\begin{array}{*{20}{l}}
  {A.\pi {r^2}h} \\
  {B.\pi rl} \\
  {C.2\pi rh} \\
  {D.2h(l + b)}
\end{array}\]

Hint: We have several objects that we come across in our daily life like measuring jars, circular pipes and circular pillars are all cylindrical in shape. Such an object having a curved (lateral) surface and congruent circular cross-section is called a circular cylinder.

Complete step-by-step answer:
Congruent circular cross section means that both the circular ends are identical and similar in their radii and circumference.
A cylinder can be classified into three basic types :
Simple cylinder: if the base is not circular then the solid is simply called a cylinder.
Circular cylinder: if the closed surface is a circle, the cylinder is called a circular cylinder.
Right circular cylinder: if the axis is perpendicular to the circular section of the cylinder is called a right circular cylinder.
 
The space occupied by the cylinder has volume and this volume is known as volume of the cylinder.
Let us take a regular circular cylinder whose radius is ‘r’ units and its height is given by ‘h’ units. Suppose the regular circular cylinder is a filled solid made of metal where its circular end is a circle whose area will be $\pi {r^2}$ . since the cylinder is ‘h’ units in height.
Therefore volume of a regular circular cylinder is given by:
$\Rightarrow \pi {r^2}h$ cubic units.
Since three units are involved so when multiplied will yield a cubic unit.
Therefore we can conclude that the correct option is A.
So, the correct answer is “Option A”.

Note: Volume is always calculated for the completely filled solids. For the cylinders that are hollow or the cylinders made out of metal or paper sheets , one can calculate surface area by adding the curved surface area and the area of two circular ends.