ANS:C - both (a) & (b)

The diffusion coefficient of a metal in a solid solution depends upon both its composition and temperature. Diffusion coefficient, often denoted as D, is a measure of how quickly atoms or molecules move through a material by diffusion. In the case of a metal in a solid solution, diffusion refers to the movement of metal atoms through the crystal lattice of the host material.

1. Composition: The diffusion coefficient can be influenced by the composition of the solid solution. Different alloying elements or impurities may affect the mobility of atoms within the lattice, leading to variations in the diffusion coefficient. The presence of other elements can introduce lattice defects, alter the crystal structure, or affect atomic bonding, all of which can impact diffusion behavior.
2. Temperature: Temperature has a significant influence on diffusion coefficients. Generally, as temperature increases, the kinetic energy of atoms also increases, leading to faster atomic motion and higher diffusion coefficients. Conversely, at lower temperatures, diffusion rates are typically slower due to reduced atomic mobility and higher lattice energy barriers.