Q1: With increase in annealing temperature, the following defect density decreases.

ANS:D - All of them

As the annealing temperature increases, the density of all three defects—vacancies, dislocations, and grain boundaries—typically decreases. Explanation:

1. Vacancies: Vacancies are atomic-scale defects where atoms are missing from the crystal lattice. Annealing at higher temperatures allows more energy to be available in the system, facilitating the migration and annihilation of vacancies. Consequently, the density of vacancies decreases as annealing temperature increases.
2. Dislocations: Dislocations are line defects in the crystal lattice caused by irregularities or misalignments in the arrangement of atoms. At higher annealing temperatures, dislocations are more mobile and have greater opportunity to move and rearrange, leading to their reduction in density over time.
3. Grain Boundaries: Grain boundaries are interfaces between adjacent crystalline grains with different orientations. During annealing at elevated temperatures, grain boundaries tend to migrate and become smoother, reducing their overall density in the material.