The average saltinity of sea water is

Options

A. 0.02%
B. `2.5%`
C. `3%`
D. `3.5%`

Answer

To determine the average salinity of seawater, we can follow these steps:

### Step 1: Understand the Concept of Salinity
Salinity refers to the concentration of salts in water, typically expressed as a percentage by mass or in parts per thousand (PPT).

### Step 2: Identify the Options Given
The options provided for the average salinity of seawater are:
- 0.02%
- 2.5%
- 3%
- 3.5%

### Step 3: Recall the Average Salinity of Seawater
From scientific knowledge, the average salinity of seawater is approximately 35 parts per thousand (PPT).

### Step 4: Convert Parts Per Thousand to Percentage
To convert parts per thousand (PPT) to percentage (%), we can use the following relationship:
\[ \text{Percentage} = \frac{\text{Parts per Thousand}}{10} \]
Thus,
\[ 35 \text{ PPT} = \frac{35}{10} = 3.5\% \]

### Step 5: Compare with the Given Options
Now, we compare our calculated value of 3.5% with the options provided.

### Step 6: Select the Correct Answer
The correct answer from the options is 3.5%.

### Final Answer
The average salinity of seawater is **3.5%** by mass.

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