12th Class Chemistry Unit 33 Water MCQs with Answers

Question 1

Which property of water is primarily responsible for its ability to resist rapid temperature changes in large aquatic ecosystems?

Accepted Answer

High specific heat capacity

Answer

Amphoteric nature

Answer

The permanent dipole

Answer

High redox potential

Question 2

A water sample is found to have a very high Biochemical Oxygen Demand (BOD). What does this most likely indicate about the water body?

Accepted Answer

High organic pollution

Answer

Highly oxygenated and healthy

Answer

High concentration of nitrates and phosphates

Answer

A high pH

Question 3

Which of the following best describes the formation of a "pollution plume"?

Accepted Answer

Discharge of heavy metal salts

Answer

Agricultural runoff

Answer

The mixture of hydrocarbons and road salts

Answer

Snowmelt through uncontaminated forest soil

Question 4

Why is Non-Point Source (NPS) pollution considered "weather-dependent" compared to Point Source pollution?

Accepted Answer

NPS pollution requires precipitation to wash diffuse surface contaminants into water bodies.

Answer

NPS pollutants are only toxic when the temperature of the water rises.

Answer

Point sources only discharge waste during specific industrial seasons.

Answer

Rainfall neutralizes the localized acute toxicity of point source plumes.

Question 5

Bacteria in aquatic sediments convert inorganic mercury into methylmercury ([CH₃Hg]⁺). Which statement best explains why this conversion increases the ecological hazard?

Accepted Answer

Methylmercury is highly fat-soluble

Answer

Methylmercury dissolves more readily in the water

Answer

Methyl mercury is biodegradable and enters nutrient cycle.

Answer

Methylmercury is a solid that clogs the gills of fish.

Question 6

Which condition is a direct result of Cadmium (Cd) replacing Calcium (Ca) in the skeletal system?

Accepted Answer

Itai-itai disease

Answer

Minamata disease

Answer

Blue Baby Syndrome

Answer

Chloracne

Question 7

What is the primary chemical role of Aluminium Sulphate (Al₂(SO₄)₃) in the wastewater treatment process?

Accepted Answer

Converting colloidal particles to floc.

Answer

To kill pathogenic bacteria.

Answer

To act as a semi-permeable membrane.

Answer

To adsorb organic contaminants.

Question 8

Ion exchange technology "softens" water by replacing calcium (Ca²⁺) and magnesium (Mg²⁺) ions with:

Accepted Answer

Sodium (Na⁺) or hydrogen (H⁺) ions

Answer

Chlorine (Cl₂) or ozone (O₃)

Answer

Aluminum (Al³⁺) or iron (Fe³⁺) ions

Answer

Carbonate (CO₃²⁻) or phosphate (PO₄³⁻) ions

Getting there and back

In school

At the gate

Fees & pay

Unit 33: Water — Mcqs