Question

1. what are the differences between density, apparent density, and bulk density of material? (concepts)
2. what are effects of environment on materials?
3. what are properties of materials related to water?
4. what are brittleness and toughness of materials?
5. what are the main technical properties of building gypsum?

Explanation:

The questions are about materials, their properties, and related concepts. The subfield "Engineering" under Natural Science is most relevant as it deals with material science and properties of building materials like gypsum, environmental effects on materials, etc.

Answer:

Natural Science - Engineering