Tag: evs

Questions Related to evs

Dissolved salts in water are important because :

evs water: a precious resource importance of water let's play with water water and its properties water resources and conservation

  1. they provide taste

  2. growth of plants

  3. minerals essential for body

  4. all of the above

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Correct Option: D
Explanation:

Dissolved salts in water are important because
(A) They provide taste
(B) Growth of plants
(C) Minerals essential for body
Water contains dissolved salts which provide taste to water for drinking purposes. Also these salts are essential for growth and development of plants. These dissolved salts provide the essential minerals which are required for growth of body.

Dissolved gases can be removed from water by:

evs water: a precious resource importance of water let's play with water water and its properties water resources and conservation

  1. chlorination

  2. boiling

  3. filtration

  4. both A and C

Show answer
Correct Option: B
Explanation:

Dissolved gases can be removed from water by boiling.
Water contains certain gases in dissolved state. The higher the temperature of a solution becomes, the less a gas dissolves provided it doesn't react with the solvent. Consequently, heating/boiling a solution can expel the remaining gas.

How many grams of water can be produced when 8 g of hydrogen react with 8 g oxygen?

evs water: a precious resource importance of water let's play with water water and its properties water resources and conservation

  1. 8 g

  2. 9 g

  3. 18 g

  4. 27 g

  5. 30 g

Show answer
Correct Option: B
Explanation:
The molecular masses of hydrogen, oxygen and water are 2 g/mole, 32 g/mole and 18 g/mole respectively.
$2H _2 + O _2 \rightarrow 2H _2O$
 $2 \times 2 = 4$ g of hydrogen reacts with  $1 \times 32 = 32$ g of oxygen to form  $2 \times 18 = 36$ g of water.
Hence, $\dfrac {4}{4} = 1$ g of hydrogen reacts with  $\dfrac {32}{4}  = 8$ g of oxygen to form  $\dfrac {36}{4}= 9$ g of water.

9 grams of water can be produced when 8 g of hydrogen reacts with 8 g oxygen.

The colour of anhydrous $CoCl _2$ is:

evs water: a precious resource importance of water let's play with water water and its properties water resources and conservation

  1. pink

  2. blue

  3. red

  4. white

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Correct Option: B
Explanation:

Anhydrous $CoCl _2$ is blue in colour.


As it absorbs water, it turns pink.

Hence,option B is correct.

The discovery of the fact that oxygen and hydrogen combine to form water, was a major step in the development of science. Who made this discovery?

evs water: a precious resource importance of water let's play with water water and its properties water resources and conservation

  1. Carl Wilhelm Scheele

  2. Isaac Newton

  3. Joseph Priestley

  4. Henry Cavendish

Show answer
Correct Option: D
Explanation:
It was the chemist Henry Cavendish (1731 – 1810), who discovered the composition of water when he experimented with hydrogen and oxygen and mixed these elements together to create an explosion (oxyhydrogen effect). In 1811, the Italian physician Amadeo Avogadro finally found the ${H} _{2}O$ formula for water.

What is the final product when oxygen and hydrogen are mixed in a test tube at room temperature?

evs water: a precious resource importance of water let's play with water water and its properties water resources and conservation

  1. Hydrogen peroxide

  2. Water

  3. A base

  4. A zwitterion

  5. No reaction takes place

Show answer
Correct Option: E
Explanation:

The gas-phase oxidation of hydrogen has been extensively studied over a wide range of temperatures and pressures.


$H _2 + \dfrac {1}{2} O _2 \rightarrow H _2O$ ,$ \Delta H^o= -242 kj/mol$
$H _2(g) + \dfrac {1}{2}O _2(g) \rightarrow H _2O(g) $        $\Delta H^o = –242 kJ/mol$

This reaction does not take place at all when the two gases are simply mixed at room temperature. 

At temperatures around 500-600°C it proceeds quite smoothly, but when heated above 700° or ignited with a spark, the mixture explodes.

Hence the correct option is E.


Which of the following is not true for the care of teeth?

evs structure and functions of living organisms -ii dental care, eye care and hair care dental care and dental diseases salivary glands

  1. We should not chew the food.

  2. We should not eat too many sweets.

  3. We should brush twice a day.

  4. We should eat raw fruits and vegetables.

Show answer
Correct Option: A
Explanation:
  • Care of the teeth should be taken by:
  1. Brush your teeth 2 times a day with fluoride (“FLOOR-ide”) toothpaste.
  2. Visit a dentist regularly for a checkup and cleaning.
  3. Cut down on sugary foods and drinks.
  4. Don't smoke or chew tobacco etc. Hence, We should not chew the food is not true for the care of teeth.
So, the correct answer is 'We should not chew the food'.

Fill the blank
Sugar + Plaque $\rightarrow$ 

evs structure and functions of living organisms -ii dental care, eye care and hair care dental care and dental diseases salivary glands

  1. Starch

  2. Enamel

  3. Acids

  4. Microbes

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Correct Option: C
Explanation:

  • Plaque is a soft, sticky film that builds up on your teeth and contains millions of bacteria. 
  • When you eat, the bacteria in plaque use the sugars in your food to produce acids that eat away at the tooth enamel. Hence, Sugar + Plaque → acids.
So, the correct answer is 'acids'. 

The soft, sticky layer formed on the tooth which is harmful is 

evs structure and functions of living organisms -ii dental care, eye care and hair care dental care and dental diseases salivary glands

  1. Enamel

  2. Plaque

  3. Dentine

  4. Pulp

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Correct Option: B
Explanation:
  • Plaque is a soft, sticky film that builds up on your teeth and contains millions of bacteria. 
  • When you eat, the bacteria in plaque use the sugars in your food to produce acids that eat away at the tooth enamel.  Hence, The soft, sticky layer formed on the tooth which is harmful is a plaque.
So, the correct answer is 'plaque'.

A dental disease characterised by mottling of teeth is due to the presence of an ingredient in drinking water, namely 

evs structure and functions of living organisms -ii dental care, eye care and hair care dental care and dental diseases salivary glands

  1. Fluorine

  2. Mercury

  3. Boron

  4. Chlorine

Show answer
Correct Option: A
Explanation:

A dental disease characterised by mottling of teeth is due to the presence of an ingredient in drinking water, namely fluorine. Dental fluorosis or mottling of tooth enamel is a developmental disturbance of dental enamel caused by the consumption of excess fluoride during tooth development. The risk of fluoride overexposure occurs at any age but it is higher at younger ages.

Therefore, the correct answer is option A.