Vacancy and interstitial defects in solids are examples of:

thermodynamic defect

The correct answer is option 2. thermodynamic defect.

Vacancy and interstitial defects in solids are primarily: Thermodynamic defects.

These defects arise inherently within the material without the introduction of foreign atoms or changes in composition. They are thermally generated due to the material's intrinsic properties at a given temperature.

Explanation:

Vacancy defects: An atom is missing from its regular lattice site, creating a localized void. This can occur through thermal vibrations, where an atom gains enough energy to overcome its bonds and leave its place.

Interstitial defects: An extra atom is squeezed into an interstitial space (between normal lattice sites) where it doesn't belong. This happens less frequently than vacancy defects but can occur when atoms from external sources or internal rearrangements migrate and end up in interstitial sites.

While vacancy and interstitial defects can sometimes lead to:

Non-stoichiometric defects: When the number of vacancies or interstitials affects the overall composition of the material, altering the stoichiometry (ideal atomic ratios). This effect is usually subtle and often not the primary characteristic of these defects.

Metal deficiency defects: If vacancies occur preferentially in metal sublattices of ionic compounds, affecting the metal-to-nonmetal ratio. This is more specific and not always applicable to all vacancy cases.

Here's a table summarizing the key points:

Impurity defects:  These specifically involve the presence of foreign atoms within the material's lattice, distinct from the intrinsic vacancy and interstitial defects.

The exact nature of the defects and their implications depend on the specific material, its atomic structure, and the external conditions (temperature, pressure, etc.).