18) The major sink(s) forCl^- in the ocean is(are):

1. Formation of authigenic minerals
2. Consumption by hydrothermal activities
3. Consumption by reverse weathering
4. Reaction in sediment pore waters
5. All of above
6. a, b and c
7. a and d
8. b and c

19) The correct sequence in theconcentration of cations in seawater is:

1. Ca²⁺> Na⁺ > Mg²⁺
2. Na⁺ > Ca²⁺ > Mg²⁺
3. Ca²⁺ < Na⁺ < Mg²⁺
4. Na⁺ > Mg²⁺ > Ca²⁺

20) The major sink(s) forMg²⁺ in the ocean is(are):

1. Formation of authigenic minerals
2. Consumption by reverse weathering
3. Consumption by hydrothermal activities
4. Reaction in sediment pore waters
5. All of above

21) The correct sequence in theconcentration of anions in seawater is:

1. Cl^- > SO₄^2- >HCO₃^-
2. SO₄^2- > Cl^- >HCO₃^-   
3. Cl^- > HCO₃^- >SO₄²
4. Na⁺ > Cl^- > HCO₃

22) The major sink(s) forNa⁺ in the ocean is(are):

1. Consumption by reverse weathering
2. Formation of authigenic minerals
3. Consumption by hydrothermal activities
4. Reaction in sediment pore waters
5. all of above
6. a and b
7. a and c
8. b and c
9. a and d

23) The major sink(s) forK⁺ in the ocean is(are):

1. Consumption by hydrothermal activities
2. Formation of authigenic minerals
3. Consumption by reversing weathering
4. Reaction in sediment pore waters
5. All of above
6. a, b and d
7. a, c and d
8. b, c and d

24) The correct sequence in oceanicresidence time is:

1. HCO₃^- > SO₄^2-> Cl^-
2. SO₄^2- > Cl^- >HCO₃^-
3. HCO₃^- < SO₄^2-< Cl^-

25) If water residence time in theocean is 20,000 years, an element with a seawater to river waterconcentration ratio of 0.5 has a oceanic residence time of:

1. 80,000 yr
2. 40,000 yr
3. 20,000 yr
4. 10,000 yr

26) The major sink(s) forHCO₃^- supplied to the ocean by river runoffis(are):

1. Reaction in sediment pore waters
2. Consumption by reversing weathering
3. Consumption by hydrothermal activities
4. Formation of authigenic minerals
5. All of above
6. a and b
7. b and c
8. b and d

27) If water residence time in theocean is 40,000 years, an element with a seawater to river waterconcentration ratio of 1.5 has a oceanic residence time of:

1. 80,000 yr
2. 60,000 yr
3. 40,000 yr
4. 10,000 yr