Q.
Metallographic ______ is a chemical technique used to highlight features of metals at microscopic levels.
Answer & Explanation
Etching is a common metallographic technique that uses chemical solutions to reveal the microstructure of metals. When a metal sample is immersed in an etchant, the surface reacts differently depending on the grain structure and phase composition of the material. This process helps to highlight features like grain boundaries, phases, and defects, allowing for detailed analysis under a microscope. Etching is crucial in materials science for examining how a material's internal structure influences its properties and performance.
Thus correct option is: D.