ANS:D - all the above.

1. Dissolved Salts: Seawater contains a variety of dissolved salts and minerals that increase its density and specific weight compared to pure water. The most abundant salt in seawater is sodium chloride (table salt), but it also contains other salts such as magnesium chloride, calcium sulfate, and potassium sulfate. These dissolved salts increase the mass of the water without significantly increasing its volume, resulting in a higher specific weight.
2. Dissolved Gases: Seawater may also contain dissolved gases, including oxygen, nitrogen, and carbon dioxide. However, the contribution of dissolved gases to the increase in specific weight of seawater is relatively small compared to dissolved salts. While dissolved gases can affect the chemical composition and properties of seawater, they do not significantly alter its density compared to pure water.
3. Suspended Matter: Seawater can contain suspended matter such as plankton, sediment, organic particles, and other debris. While suspended matter can affect the appearance and clarity of seawater, it generally has a negligible impact on the overall specific weight of seawater. The particles in suspended matter are typically small and do not significantly alter the density of the water.