Arrange the following major constituents of ocean water (over 100 ppm) in decreasing order of their percentages:

A. Chlorine
B. Sulfates
C. Sodium
D. Magnesium

Choose the correct answer from the options below:

Correct option is B

The major constituents of ocean water (in decreasing order of their percentages) are:

Chlorine (A) - ~55%

• Present as chloride ions (Cl⁻), making seawater salty.
• Source: Weathering of rocks & volcanic activity.

Sodium (C) - ~30.6%

• Found as sodium ions (Na⁺).
• Combines with chloride to form sodium chloride (NaCl - common salt).

Sulfates (B) - ~7.7%

• Present as sulfate ions (SO₄²⁻).
• Essential for marine life and biochemical cycles.

Magnesium (D) - ~3.7%

• Found as magnesium ions (Mg²⁺).
• Important for marine organisms and coral formation.

Thus, the correct decreasing order is:
A (Chlorine) → C (Sodium) → B (Sulfates) → D (Magnesium)

Why is Ocean Water Salty?

• Salt in the ocean comes from weathering of rocks, hydrothermal vents, and volcanic eruptions.
• NaCl (Sodium Chloride) is the most abundant salt, making seawater taste salty.

Importance of Ocean Salinity:

• Affects ocean circulation and climate.
• Essential for marine ecosystems.
• Influences density and ocean currents (e.g., thermohaline circulation).