Specific surface area (SSA) in particle technology is defined as the total surface area available per unit of what fundamental basis? Choose the definition that matches standard engineering usage for powders and porous solids.

Introduction / Context:
Specific surface area (SSA) is a cornerstone property in particle technology, powder processing, catalysis, and adsorption. It quantifies how much surface is available for reaction, dissolution, or interfacial phenomena relative to a defined amount of material. Correctly stating the basis for SSA is essential for interpreting BET measurements, dissolution rates, and reaction kinetics across industries such as cement, ceramics, pigments, pharmaceuticals, and catalysts.

Given Data / Assumptions:

• SSA is reported as surface area divided by a quantity of solid.
• Common reporting units in engineering practice are m^2/g or m^2/kg.
• Powders may also be characterized on a volumetric basis in some niche contexts, but the standard basis requested here is the widely accepted one for general use.

Concept / Approach:
SSA is conventionally defined as surface area per unit mass. Gas adsorption methods (e.g., nitrogen BET) produce results normalized to sample mass because mass is easy to measure precisely and is independent of particle packing or porosity in the measurement cell. While a surface area per unit volume can be constructed (e.g., “surface-to-volume ratio”), the term “specific surface area” almost universally implies per mass in standard practice.

Step-by-Step Solution:
Identify standard units used in labs and datasheets: m^2/g or m^2/kg.Recognize that these units are surface area divided by mass, not volume.Select the option that explicitly names mass (weight) as the basis.

Verification / Alternative check:
Material safety data sheets, catalyst specifications, cement and pigment technical data commonly list SSA in m^2/g (BET). This consistent industry usage verifies the mass basis as the standard definition for SSA.

Why Other Options Are Wrong:
Volume: “Surface area per unit volume” is used in some geometric analyses but is not the conventional definition of SSA in process industries.Either (a) or (b): Too broad; the question requests the standard engineering definition.Neither (a) nor (b): Incorrect because SSA must be normalized to a quantity, and mass is the standard.

Common Pitfalls:
Confusing “surface-to-volume ratio” with “specific surface area.” The former is geometry-centric; the latter, in practice, is mass-normalized. Also avoid mixing units (e.g., reporting m^2 without dividing by g or kg).

Final Answer:
Weight (mass)