Answer : 2. "3.5%"
Explanation :

Answer: B) 3.5% Explanation: Seawater or salt water is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of approximately 3.5% or 35 parts per thousand. This means that for every 1 litre (1000 mL) of seawater there are 35 grams of salts dissolved in it.   Hence, The average salinity of seawater is 3.5%.