Answer: Ca 2+ and Mg 2+ ions.
- A Na+ and K+ ions
- B Ca<sup>2+</sup> and Mg<sup>2+</sup> ions
- C Cl- ions
- D Dissolved oxygen
Correct answer: B. Ca<sup>2+</sup> and Mg<sup>2+</sup> ions
Explanation: Soaps form an insoluble precipitate with Ca<sup>2+</sup> and Mg<sup>2+</sup> ions present in hard water, reducing their cleaning efficiency. Synthetic detergents avoid this problem.
The hydrophobic hydrocarbon tail of each soap/detergent molecule dissolves into an oily dirt droplet, while the hydrophilic (ionic) head stays in the surrounding water - trapping the grease inside a micelle that rinses away with water.
Concept context
Drugs and how they interact with biological targets, chemicals in food, and cleansing agents (soaps and detergents) - chemistry applied directly to daily life and healthcare.