Chemistry 9th Chap 12 : Topic 2 - Maryam Publications

Chemistry Chapter 12 : Topic 2

Beneficial Substances in Water

1 / 20

Natural water contains dissolved oxygen, which is essential for aquatic ecosystems. Which statement best explains its role?

A) It supports respiration of fish and other aquatic organisms.

B) It removes dissolved minerals from water.

C) It increases water temperature and speeds up evaporation.

D) It reacts with salts to form pure water.

2 / 20

Why is dissolved oxygen considered a naturally beneficial substance in water?

A) It is required for survival of aquatic organisms.

B) It kills harmful bacteria in water.

C) It prevents all types of pollution.

D) It makes water chemically pure.

3 / 20

Some metal compounds in natural water are beneficial because they:

A) Increase the boiling point of water

B) Always make water safe for drinking

C) Remove harmful gases from water

D) Provide essential trace minerals needed by living organisms

4 / 20

Which of the following best describes the role of trace metal ions in natural water?

A) They are always toxic and must be removed completely.

B) They act as essential nutrients in very small amounts.

C) They convert water into a pure substance.

D) They have no biological importance.

5 / 20

Why can iron compounds in water sometimes be beneficial?

A) They increase oxygen production in water.

B) They sterilize water naturally.

C) They help in photosynthesis of aquatic plants.

D) They provide essential iron required for blood formation in animals.

6 / 20

Which statement correctly differentiates beneficial substances from harmful ones in natural water?

A) Beneficial substances are those that increase pollution.

B) Beneficial substances are needed in controlled amounts for life processes.

C) Only gases in water are beneficial.

D) All dissolved substances are harmful.

7 / 20

Calcium compounds in natural water are important because they:

A) Help in strengthening bones and shells of organisms

B) Remove oxygen from water

C) Cause water to become acidic

D) Increase toxicity of water

8 / 20

Magnesium ions present in water are beneficial because they:

A) Convert water into a gas

B) Are essential for chlorophyll formation in plants

C) Destroy aquatic life

D) Reduce dissolved oxygen

9 / 20

Why are naturally occurring mineral ions in water not always harmful?

A) They evaporate quickly.

B) They are required in trace amounts for biological functions.

C) They are chemically inactive.

D) They are always diluted beyond usefulness.

10 / 20

Which of the following is an example of a beneficial dissolved substance in water?

A) Plastic particles

B) Sewage waste

C) Mercury compounds

D) Dissolved oxygen

11 / 20

What is the significance of balanced mineral content in natural water?

A) It eliminates all microbes.

B) It supports biological processes in living organisms.

C) It makes water completely pure.

D) It increases water hardness only for industrial use.

12 / 20

Why is excessive removal of all minerals from drinking water not ideal?

A) It causes water to evaporate.

B) It increases pollution.

C) It reduces essential nutrients needed by the body.

D) It makes water radioactive.

13 / 20

Which of the following correctly explains the role of dissolved oxygen in water ecosystems?

A) It is used in respiration by aquatic organisms.

B) It increases salinity of water.

C) It converts water into hydrogen gas.

D) It causes corrosion of metals only.

14 / 20

Natural water containing trace minerals is considered beneficial because it:

A) Loses all dissolved gases

B) Provides essential nutrients for organisms

C) Becomes chemically unstable

D) Becomes toxic automatically

15 / 20

Which statement best describes the dual nature of substances in natural water?

A) Some substances are beneficial in small amounts while others are harmful in excess.

B) All substances are harmful.

C) Water contains only gases.

D) All substances are beneficial.

16 / 20

Why is magnesium in water considered biologically important?

A) It increases water hardness only.

B) It removes oxygen from water.

C) It kills bacteria in water.

D) It is a part of chlorophyll in plants.

17 / 20

Which of the following is TRUE about beneficial substances in water?

A) They are required in controlled trace amounts.

B) They are always organic compounds.

C) They are useful only in large concentrations.

D) They are never naturally occurring.

18 / 20

What happens if dissolved oxygen level in water decreases significantly?

A) No change occurs

B) Water becomes distilled

C) Aquatic life thrives more

D) Aquatic organisms may suffocate

19 / 20

Why is natural water considered a mixture of beneficial and harmful substances?

A) Because it has no dissolved gases.

B) Because it contains only salts.

C) Because it includes essential nutrients and potential pollutants.

D) Because it is always polluted.

20 / 20

Which best explains why some metal compounds in water are beneficial?

A) They increase evaporation rate.

B) They eliminate all bacteria.

C) They act as essential micronutrients for living organisms.

D) They always purify water.

Your score is

0%