Chemistry (Part-VI)

21. At what pH value does the tooth starts to decay? [S.S.C. Online MTS (T-I) 8.08.2019]

(a) 5.5
(b) 6.5
(c) 11.2
(d) 7.5

Correct Answer: (a) 5.5

Solution:Tooth decay affects the teeth when the stagnant saliva inside the mouth becomes acidic beyond a certain limit. A liquid is said to be acidic when the pH value is less than 7. Therefore, it has been found that when the pH value is around 5.5, enough acidic property is produced in the saliva, which causes damage to the teeth.

22. Removal of carbon particles from air involves the principle- [S.S.C. Online Graduate Level (T-I) 9.09.2016]

(a) Precipitation
(b) Filtration
(c) Electrophoresis
(d) Sedimentation

Correct Answer: (c) Electrophoresis

Solution:Electrophoresis is the process of removing particles from a fluid by applying an electric field, causing charged particles to move towards the electrode with the opposite charge. In the context of removing carbon particles from air, the carbon particles are given a charge, and then they are attracted to a collector plate under the influence of an electric field.

23. Sea water is a rich source of which of the following chemical elements? [S.S.C. JE Mechanical Exam 22.03.2021]

(a) Bromine
(b) Hydrogen Peroxide
(c) Cadmium
(d) Hydrogen sulphide

Correct Answer: (a) Bromine

Solution: Bromine - Sea water contains various dissolved salts, and bromine is one of the chemical elements that can be economically extracted from it on a large scale.

24. Brown stains in vessels and clothes indicate the presence of high quantities of in water. [S.S.C. Online Graduate Level (T-I) 9.09.2016]

(a) Magnesium
(b) Calcium
(c) Manganese
(d) Chromium

Correct Answer: (c) Manganese

Solution: Manganese - High quantities of manganese in water can cause brown or black stains on vessels and clothes. Iron can also cause reddish-brown stains.

25. Which is the most economical method of removing solid matter from water? [S.S.C. Online CHSL (T-I) 1.02.2017]

(a) Using deactivated carbon
(b) Electrolysis
(c) Distillation
(d) Sedimentation

Correct Answer: (d) Sedimentation

Solution:Sedimentation - Sedimentation is a cost-effective method where solid particles in water are allowed to settle out due to gravity. This process is often used as a primary step in water treatment to remove larger suspended solids before further purification.

26. _______ is a process in which impure water is boiled and the steam is called and condensed in a separate container, leaving many of the solid contaminants behind. [S.S.C. Online CGL (T-I) 23.08.2021]

(a) Decantation
(b) Distillation
(c) Sedimentation
(d) Filtration

Correct Answer: (b) Distillation

Solution: Distillation - Distillation is indeed the process described, where impure water is boiled, and the resulting steam is collected and condensed in a separate container, leaving behind many non-volatile contaminants.

27. Every hot object emits ______ . [S.S.C. Online Graduate Level (T-I) 9.09.2016]

(a) X-rays
(b) Visible light
(c) Infrared rays
(d) Ultraviolet rays

Correct Answer: (c) Infrared rays

Solution: Infrared rays - Every object with a temperature above absolute zero emits electromagnetic radiation. Hot objects, including humans, primarily emit infrared radiation, which we perceive as heat.

28. Alcohol is more volatile than water because is lower than water _________ . [S.S.C. Online Graduate Level (T-I) 11.09.2016]

(a) its boiling point
(b) its density
(c) ita viscosity
(d) its surface tension

Correct Answer: (a) its boiling point

Solution:Its boiling point - Alcohol is more volatile than water because it has a lower boiling point. Volatility refers to how easily a liquid evaporates. Liquids with lower boiling points require less energy to overcome intermolecular forces and transition into the gaseous phase.

29. Super cooling stands for cooling of a liquid: [S.S.C. Online Graduate Level (T-I) 11.09.2016]

(a) at freezing point
(b) below freezing point
(c) at melting point
(d) above melting point

Correct Answer: (b) below freezing point

Solution:Below freezing point - Supercooling is the phenomenon where a liquid is cooled below its normal freezing point without solidifying. This metastable state can occur if there are no nucleation sites for crystal formation.

30. Which of the following is not soluble in water? [S.S.C. Online Graduate Level (T-I) 29.08.2016]

(a) Lead Sulphate
(b) Zinc Sulphate
(c) Potassiut vulphate
(d) Sodium Sulphate

Correct Answer: (a) Lead Sulphate

Solution: Lead Sulphate - Lead sulfate (

PbSO₄

) is known to be largely insoluble in water. Zinc sulfate (

ZnSO₄

), potassium sulfate

K₂ SO₄

), and sodium sulfate (

Na₂ SO₄

) are all soluble in water.