The correct answer is option 1: sodium and potassium salt.

Protoplasm is the living substance found inside cells, and it is composed of both organic and inorganic components. In an animal cell, the most abundant inorganic constituent of protoplasm is sodium and potassium salt.

Sodium and potassium ions are essential for various cellular processes, such as maintaining cell volume, regulating pH levels, and conducting nerve impulses. These ions play a crucial role in the functioning of the cell membrane and the transmission of signals between cells.

Water (option 2) is indeed a major component of protoplasm, but it is not an inorganic constituent. Water is considered an inorganic compound, but it is present in both living and non-living matter.

Iron (option 3) is an essential mineral required for various cellular functions, but it is not the most abundant inorganic constituent of protoplasm in animal cells.

Phosphate (option 4) is also an important inorganic molecule found in protoplasm, but it is not the most abundant constituent in animal cells.

Therefore, the correct answer is option 1: sodium and potassium salt.