An angle is made up of two rays having a common endpoint.
The two rays forming the angle are called 'sides' or 'arms' of the angle, and the common endpoint is called the 'vertex' of the angle.

Property: 1 Mark
Application: 1 Mark
According to the property of parallel lines, the distance between them is always constant.
Navi is correct because the distance between the railway lines is always constant.

Each option: 1 Mark
(i)  Points in figure (i) are A, B and C. The line segments are AB, BC, and AC. 

(ii)   Points in figure (ii) are A, B, C and D. The line segments are AB, BC, CD and DA.

(iii)   Points in figure (iii) are A, B, C, D and E. The line segments are AB, BC, CD, DE and AE.

Definition: 1 Mark
Example: 1 Mark
A ray is a portion of a line. It starts at one point (called starting point) and goes endlessly in a direction.
The various other rays which we observe are Sun rays, rays coming from the headlight of cars, etc.

Definition: 2 Marks
Properties: 2 Marks
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 A radius is a line segment that connects the centre to a point on the circle.

The diameter is a straight line which starts at one point of the circle, goes through the centre and ends on the other point.

A chord of a circle is a straight line segment whose endpoints both lie on the circle.

Following are the properties of chords of a circle:

1. Chords are equidistant from the centre only if their lengths are equal.

2. A chord that passes through the centre of a circle is called a diameter, and it is the longest chord.

Definition: 1 Mark
Explanation: 1 Mark
Example: 1 Mark

A quadrilateral is a type of polygon. It has four sides.
Quadrilateral means "four sides" (quad means four, lateral means side).

It is a 2-dimensional closed shape and has straight sides.

In the quadrilateral, ABCD, here (AB, BC), (BC, CD), (CD, DA) and (DA, AB) are the adjacent side whereas (AB, CD) and (AD, BC) are the opposite sides.
The four angles are $\angle$ABC, $\angle$BCD, $\angle$CDA, $\angle$DAB. 

Angles: 1 Mark
Sides: 1 Mark
Diagonals: 1 Mark

In the given figure the opposite angles are (∠DAB,∠BCD) & (∠ADC, ∠ABC).
The side DA is opposite to BC, and the side CD is opposite to AB.
AC and BD are the diagonals.