Q1: Which of the following is generally considered as opaque surface towards radiations?

ANS:D - Both (b) and (c)

Solids Explanation:

1. Gases: Gases are generally considered transparent to many types of radiation, including visible light and infrared radiation. While some gases may absorb certain wavelengths of radiation, they are often considered less opaque compared to solids and liquids.
2. Solids: Solids are typically opaque to radiation. When radiation strikes a solid surface, it tends to be absorbed or reflected rather than transmitted through the material. This absorption of radiation contributes to heating the solid object.
3. Liquids: Liquids can vary in their opacity depending on their composition and density. Some liquids may be transparent to certain wavelengths of radiation, while others may be more opaque. However, in general, liquids are less opaque compared to solids.