### Series

1.

Explanation:

In each step, the pin rotates 90oCW and the arrow rotates 90oACW.

2.

Explanation:

One, two, three, one, two, three…..arcs get inverted sequentially. This inversion takes place in an ACW direction.

3.

Explanation:

The pin rotates 45oCW and 90oCW alternately and moves one space (each space is equal to half-a-side of the square) and two spaces CW alternately. The arrow rotates 90oACW and 45oACW alternately and moves two spaces and one space.

4.

Explanation:

In each step, the CW-end element moves to the ACW-end position.

5.

Explanation:

In each step, the elements move in the sequence.

6.

Explanation:

In one step, the existing element enlarges and a new element appears inside this element. In the next step, the outer element is lost.

7.

Explanation:

In One step, the middle element rotates through 180o and in the next step, the other two elements rotate through 180o. The two steps are repeated alternately.

8.

Explanation:

One arc and four arcs get inverted alternately.

9.

Explanation:

The ‘T’ shaped large element rotates 90oCW in each step. The two small symbols interchange positions and the symbol that reaches the upper position gets replaced by a new one.

10.

Explanation:

In each step, element at the upper-right position gets enlarged, inverts vertically and reaches the lower-left corner; the existing element at the lower-left position, is lost and a new small element appears at the upper-right position.

11.

Explanation:

In the first step, the lowermost line segment is converted into a curve. In the second step, the second line segment also gets converted into a curve and the (existing curve is inverted. In each subsequent step, all the elements (line segments and curves) move in the sequence

12.

Explanation:

The number of parts increases by one along with the number of sides in the figure.

13.

Explanation:

All the elements move half-a-side of the square boundary in ACW direction in each step. Also, first, third and fifth elements are replaced by new elements in one step and second, fourth and sixth elements are replaced by new elements in the next step. The two steps are repeated alternately.

14.

Explanation:

In each step, the dot moves one space CW and the arrow moves two spaces CW.

15.

Explanation:

In one step, the figure gets laterally inverted and one line segment is lost from the upper end of the RHS portion of the figure. In the next step, the figure gets laterally inverted and one line segment is lost from the upper end of the LHS portion of the figure.

16.

Explanation:

The elements move in the sequence’s  and  alternately.

17.

Explanation:

In the first step, the ACW end element moves two spaces (each space is equal to half-a-side of the square boundary) in an ACW direction. In the second step, the CW-end element moves three spaces ACW. In the third step, the remaining element moves four spaces ACW. The three steps are repeated to continue the series.

18.

Explanation:

The central arrow rotates 90oACW and 45oCW alternately. The half-arrow moves half-a-side of the square boundary in a CW direction and its head turns to the other side of the line in each step.

19.

Explanation:

Both the larger and the smaller squares move to the adjacent corner ACW in each turn. Also, the shading in the smaller square moves 1, 2, 3, 4, 5, … steps ACW sequentially and the shading in the larger square moves 1, 2, 3, 4, 5,…. steps CW sequentially.

20.