# DBT JRF 2022 — Question 141

Exam: DBT JRF 2022 · Section: B · Topic: Environmental Science › Aquatic Chemistry - Saline Water Cations · Difficulty: Medium

## Question

Arrange these soluble cations (Na, Ca, K, Mg) in ascending order of abundance of soluble cations found in saline water bodies:

## Options

- **A.** Na > Mg > Ca > K
- **B.** Mg > Na > Ca > K
- **C.** K > Mg > Ca > Na
- **D.** Na > Mg > K > Ca

## Answer

Option A

## Explanation

Soluble cation abundance in saline water: $\text{Na} > \text{Mg} > \text{Ca} > \text{K}$ : Seawater (the reference saline water body) contains these major cations with approximate concentrations: • Sodium (Na⁺): ~10,800 mg/L (470 mM) — BY FAR the most abundant • Magnesium (Mg²⁺): ~1,290 mg/L (53 mM) • Calcium (Ca²⁺): ~412 mg/L (10 mM) • Potassium (K⁺): ~399 mg/L (10 mM) Ascending order (lowest to highest): $K < Ca < Mg < Na$ Equivalently: $Na > Mg > Ca > K$ (from most to least abundant). This order is important for: • Understanding osmotic balance in marine organisms. • Biogeochemistry of ocean water chemistry. • Marine biotechnology applications. Answer: Ascending order of abundance: K < Ca < Mg < Na (i.e., Na > Mg > Ca > K from most to least).

Source: https://mypyqbuddy.com/questions/arrange-these-soluble-cations-na-ca-k-mg-6a104cd5920734408bc0c79c