In the case of solid, number of degrees of freedom is:

• A. 3
• B. 5
• C. 6
• D. 7

In the context of solid materials, the number of degrees of freedom refers to the ways in which the particles can move. For a solid, the relevant degrees of freedom are typically associated with the motion of atoms or molecules.

Degrees of Freedom in Solids

For a solid, each atom can move in three-dimensional space, which gives it three translational degrees of freedom. However, in addition to translation, atoms can also rotate about their axes, but this is generally limited in solids due to their fixed positions in the lattice structure.

Options Explained

• A. 3: This represents only translational motion.
• B. 5: This could imply some rotational motion but is not standard for solids.
• C. 6: This includes three translational and three rotational degrees of freedom.
• D. 7: This is not applicable to solids.

Therefore, the correct answer is C. 6, which accounts for three translational and three rotational degrees of freedom in a solid structure.