Q1: The point about which combined motion of rotation and translation of a rigid body takes place, is known as

ANS:B - Instantaneous centre

The point about which combined motion of rotation and translation of a rigid body takes place is known as the "Instantaneous centre." The instantaneous center is a concept used in the study of the kinematics of rigid bodies. It is the point at which the velocities of all points on the body are parallel to each other at any instant in time. This point is pivotal because, at any given instant, a rigid body can be considered to rotate about the instantaneous center with pure rotation and to translate with pure translation. The combined motion of rotation and translation is effectively simplified to just rotation about the instantaneous center. Therefore, the correct answer to your question is: "Instantaneous centre."