Q1. A square is a type of rhombus, as it has four equal sides, two of which are definitely parallel to each other. We cannot say that a rhombus is a square even though both have four equal sides. This is because rhombus does not have right angles, unlike squares, which have four right angles, particularly due to the fact that they are tilted.
Q2. All of the given statements are correct. A square and parallelogram are quadrilaterals as they have four sides. The opposite sides of a square and a parallelogram are parallel, no doubt. A trapezium has only one parallel line; it is true as the top and bottom sides are parallel. The lines at the side, however, are going further or nearer to each other, depending on how it is viewed. Therefore, all statements are correct.
Q3. A trapezium has one pair of opposite sides equal in length. The opposite sides are those which are not parallel to each other. The quadrilateral has a pair of opposite angles that are supplementary, due to two sides that are not equal to each other in terms of lengths.