ANS:D - none of these

If heat transfer rate varies with time, it is termed as none of these options provided. Explanation:

• Forced convection refers to heat transfer due to the movement of fluid, typically driven by external factors such as pumps or fans. The variation of heat transfer rate with time is not inherently related to forced convection.
• Steady-state conduction refers to a situation where the temperature distribution within a solid does not change with time. While heat transfer rate may remain constant in steady-state conduction, it does not necessarily vary with time.
• Monochromatic radiation refers to radiation consisting of a single wavelength. The variation of heat transfer rate with time is not specific to monochromatic radiation.

When the heat transfer rate varies with time, it suggests a dynamic process where the temperature distribution and heat flux change over time. This could occur, for example, during transient conduction, unsteady-state convection, or time-varying radiation processes. Therefore, the term to describe heat transfer rate varying with time would depend on the specific nature of the process and would not fit into any of the provided options.