Q1: Solid angle subtended by the finite surface at the radiating element is

ANS:B - called the angle of vision.

"called the angle of vision" is not an accurate description of the concept in question in the context of radiation heat transfer. The "angle of vision" typically refers to the angular extent of the field of view perceived by an observer or a camera. It is unrelated to the concept of the solid angle subtended by a surface at a radiating element, which is known as the view factor in radiation heat transfer. Therefore, the correct term for describing the solid angle subtended by a finite surface at a radiating element in radiation heat transfer analysis is the view factor, not the "angle of vision."