Ans :- Postulate – I

A straight line segment can be formed by joining any two points in space.

In Geometry, a line segment is a part of a line that is bounded by 2 distinct points on either end. It consists of a series of points bounded by the two endpoints. Thus a line segment is measurable as the distance between the two endpoints. A line segment is named afterthe two endpoints with an overbar on them.

Postulate – II

Any straight line can be extended indefinitely on both sides. Unlike a line segment, a line is not bounded by any endpoint and so can be extended indefinitely in either direction. A line is uniquely defined as passing through two points which are used to name it.

Postulate – III

A circle can be drawn with any centre and any radius. For any line segment, a circle can be drawn with its centre at one endpoint and the radius of the circle as the length of the line segment. Consider a line segment bounded by two points. If one of these points is taken as the centre of a circle and the radius of the circle is taken as equal to the length of the segment, a circle canbe drawn with its diameter twice than the length of the line segment.

In the above example, the line segment AO serves as the radius of a circle with centre at point O and a diameter equal to AB wherel(AB) =2l(AO).

Postulate – IV

All right angles are congruent or equal to one another. A right angle is an angle measuring 90 degrees. So, irrespective of the length of a right angle or its orientation all right angles are identical in form and coincide exactly when placed one on top of the other.

A right angle

Postulate – V

Two lines are parallel to each other if they intersect the third line and the interior angle between them is 180 degrees.

'Parallel lines’ are a set of 2 or more lines that never cross or intersect each other at any point in space if they are extended indefinitely. As you can see in the above image, line 1 and line 2 are parallel if and only if the sum of angles ‘a’ and ‘b’ they make with thetransversal is 180 degrees.