Explanation:
Percentage w/v means that weight of solute present in 100 ml of a solution. Hence, 15% w/v means that 15 gram of solute per 100 ml of solution.
Hence, for 2 L (or 2000 mL) preparation the amount of mass will be calculated as follows.

= 300 g
Thus, we can conclude that weight of Tris-HCL required is 300 g.
The correct answer is E. A cell
Explanation:
The cell is the smallest unit of life that exists and that constitutes all living organisms and body tissues including unicellular and multicellular organisms. Due to this, cells are considered as the fundamental unit of life as even the smallest and simplest living organisms are made of cells or at least made of one cell.
Cells are commonly made up of three main parts: the cell membrane which surrounds the cell and controls the substances that enter and leave it; the nucleus which is the structure within the cell that contains the nucleolus and most of the cell's DNA; and the cytoplasm that is the fluid inside the cell that contains other tiny cell particles with specific functions, such as the Golgi apparatus, mitochondria, and the endoplasmic reticulum. This applies to all cells except to prokaryotic cells because these do not contain a nucleus but a chromosome in the middle of the cell.
The answer to number 4 is D
Homeostasis is the process by which organisms maintain internal environment constant. Anaplasia is the lack of differentiation of neoplastic cells. Histology is the study of the microscopic structures of tissues and a histologist is a person who has studied histology. Atresia is the absence of a normal opening or failure of a structure to be tubular. Therefore the correct answer is Homeostasis