If you cover 360${}^{\circ }$ of the track , the length covered = 400m
So,
For 180${}^{\circ }$, the length covered will be
                     $=\frac{1}{2}\left(400m\right)=200m$
For 90${}^{\circ }$, the length covered will be 
                     $=\frac{1}{2}\left(200m\right)=100m$
$\therefore$ For 270${}^{\circ }$, the length covered = length covered for 180${}^{\circ }+$  length covered for 90${}^{\circ }$
       $=200m+100m=300m$

We can see the angle between north and south direction is 180${}^{\circ }$.

Just by observing and comparing, we can say that roller resembles the shape of the cylinder.

In a scalene triangle, all the sides are unequal in length.

Yes, it is a polygon, a closed figure bounded by sides. Number of sides is 9. So, it is called Nonagon.

False.

If two lines are perpendicular to the same line then the two lines are parallel to each other. AB and CD are perpendicular to PQ. So, AB and CD are parallel to each other.

If  the sides of a triangles are equal , then the angle opposite to it will also be equal. Hence if two sides are equal , then the two angles opposite to the equal sides will also be equal. 

An obtuse angle is greater than 90${}^{\circ }$and less than 180${}^{\circ }$. If the angle is 180${}^{\circ }$, then it is called a straight angle.

A tetrahedron has 6 edges. Two tetrahedrons will have 12 edges. After sticking them, 3 edges will be common. So, number of edges = 12 - 3 = 9

1 - c (as the sides are not equal)

2 - a (as two sides are equal)

3 - b (as all sides are equal)