ANS:D - Temperature difference between the two surfaces of the wall.

The most important factor on which the heat conducted through a wall in a unit time will depend is the temperature difference between the two surfaces of the wall. Explanation:

1. Fourier's Law: The rate of heat transfer through a material is described by Fourier's law of heat conduction, which states that the rate of heat transfer (Q) is directly proportional to the temperature gradient (dxdT​) across the material. Q=−kAdxdT​ where:
   • Q is the rate of heat transfer,
   • k is the thermal conductivity of the material,
   • A is the cross-sectional area perpendicular to the direction of heat flow,
   • dxdT​ is the temperature gradient.
2. Temperature Difference: The temperature difference between the two surfaces of the wall is a driving force for heat transfer. The greater the temperature difference, the higher the rate of heat transfer through the wall.
3. Other Factors: While factors such as the thickness of the wall, the area of the wall perpendicular to heat flow, and the material of the wall also influence the rate of heat transfer, the temperature difference is typically the most significant factor determining the magnitude of heat transfer in a given situation.
4. Importance of Temperature Difference: The temperature difference drives heat transfer by establishing a gradient across the material. It represents the energy imbalance between the two surfaces and determines the direction and magnitude of heat flow to achieve thermal equilibrium.