Chemistry

Which of the following conditions shows the polluted environment?
(i) pH of rainwater is 5.6.
(ii) Amount of carbon dioxide in the atmosphere is 0.03%.
(iii) Biochemical oxygen demand 10 ppm.
(iv) Eutrophication.

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Contributor-Level 10

This is a Multiple choice Questions as classified in NCERT Exemplar

Options (iii) and (iv) are correct since clean water has BOD less than 5 ppm and polluted water has BOD value higher than 5 ppm. So, 10 BOD means highly polluted water. This process in which nutrient enriched water bodies support a dense plant population, which kills animal life by depriving it of oxygen and results in subsequent loss of biodiversity is termed as Eutrophication.

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10 months ago

Which of the following practices will not come under green chemistry?
(i) If possible, making use of soap made of vegetable oils instead of using synthetic detergents.
(ii) Using H₂O₂for bleaching purpose instead of using chlorine based bleaching agents.
(iii) Using bicycle for travelling small distances instead of using petrol/diesel-based vehicles.
(iv) Using plastic cans for neatly storing substances.

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Contributor-Level 10

This is a Multiple choice Questions as classified in NCERT Exemplar

Option (iv)

Using plastic cans for neatly storing substances is correct since use of plastic cans for neatly storing substances will not come under green chemistry because plastic is non-biodegradable and causes pollution.

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10 months ago

Which of the following statements is correct?
(i) Ozone hole is a hole formed in the stratosphere from which ozone oozes out.
(ii) Ozone hole is a hole formed in the troposphere from which ozone oozes out.
(iii) Ozone hole is thinning of the ozone layer of the stratosphere at some places.
(iv) Ozone hole means vanishing of the ozone layer around the earth completely.

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Contributor-Level 10

This is a Multiple choice Questions as classified in NCERT Exemplar

Option (iii)

Ozone hole is thinning of the ozone layer of the stratosphere at some places is correct since it was found that a unique set of conditions were responsible for the ozone hole. In summer, nitrogen dioxide and methane react with chlorine monoxide and chlorine atoms forming chlorine sinks, preventing much ozone depletion, whereas in winter, special types of clouds called polar stratospheric clouds are formed over Antarctica.

Following reactions occur in the stratosphere.

CF₂Cl₂→CF₂Cl + Cl?

Cl? +O₃→ClO? + O₂

ClO? + [ O ] →Cl? + O₂

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10 months ago

The pollutants which come directly in the air from sources are called primary pollutants. Primary pollutants are sometimes converted into secondary pollutants. Which of the following belongs to secondary air pollutants?
(i) CO
(ii) Hydrocarbon
(iii) Peroxyacetyl nitrate
(iv) NO

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Contributor-Level 10

This is a Multiple choice Questions as classified in NCERT Exemplar

Option (iii) Peroxyacetyl nitrate is correct since,

NO₂ (g) NO (g)+ [ O ] (i)

Oxygen atoms are very reactive and combine with the O₂ in air to produce ozone.

[ O ] +O₂ (g)→O₃ (g) (ii)

The ozone formed in the above reaction (ii) reacts rapidly with the NO (g) formed in the reacti

...more

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10 months ago

Dinitrogen and dioxygen are main constituents of air, but these do not react with each other to form oxides of nitrogen because _________.
(i) The reaction is endothermic and requires very high temperatures.
(ii) The reaction can be initiated only in presence of a catalyst.
(iii) Oxides of nitrogen are unstable.
(iv) N₂ and O₂are unreactive.

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Contributor-Level 10

This is a Multiple choice Questions as classified in NCERT Exemplar

Option (i) the reaction is endothermic and requires very high temperature is correct since dinitrogen and dioxygen are the main constituents of air. These gases do not react with each other at a normal temperature. The dissociation energy of N₂is very high due to the presence of triple bond and it is very stable.

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10 months ago

The gaseous envelope around the earth is known as the atmosphere. The lowest layer of this is extended up to 10 km from sea level, this layer is _________.
(i) Stratosphere
(ii) Troposphere
(iii) Mesosphere
(iv) Hydrosphere

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Contributor-Level 10

This is a Multiple choice Questions as classified in NCERT Exemplar

Option (ii) Troposphere is correct since the lowest region of atmosphere in which the human beings along with other organisms live is called troposphere. It extends up to the height of approximately 10 km from sea level.

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10 months ago

Match the items given in Column I and Column I

Column I	Column II
(i) Saturated solution	(a) Solution having same osmotic pressure at a given temperature as that of given solution.
(ii) Binary solution	(b) A solution whose osmotic pressure is less than that of another.
(iii) Isotonic solution	(c) Solution with two components.
(iv) Hypotonic solution	(d) A solution which contains maximum amount of solute that can be dissolved in a given amount of solvent at a given temperature
(v) Solid solution	(e) A solution whose osmotic pressure is more than that of another.
(vi) Hypertonic solution	(f) A solution in solid phase.

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Payal Gupta

Contributor-Level 10

This is a matching answer type question as classified in NCERT Exemplar

(i)- (d); (ii)- (c); (iii)- (a); (iv)- (b); (v)- (f); (vi)- (e)

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10 months ago

Match the items given in Column I and Column I

Column I	Column II
(i) Saturated solution	(a) Solution having same osmotic pressure at a given temperature as that of given solution.
(ii) Binary solution	(b) A solution whose osmotic pressure is less than that of another.
(iii) Isotonic solution	(c) Solution with two components.
(iv) Hypotonic solution	(d) A solution which contains maximum amount of solute that can be dissolved in a given amount of solvent at a given temperature
(v) Solid solution	(e) A solution whose osmotic pressure is more than that of another.
(vi) Hypertonic solution	(f) A solution in solid phase.

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10 months ago

Colligative properties are observed when _____________.

(i) A nonvolatile solid is dissolved in a volatile liquid.

(ii) A nonvolatile liquid is dissolved in another volatile liquid.

(iii) A gas is dissolved in nonvolatile liquid.

(iv) A volatile liquid is dissolved in another volatile liquid.

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Payal Gupta

Contributor-Level 10

This is a multiple choice answer as classified in NCERT Exemplar

(i) and (ii)

Colligative properties are observed when a non-volatile solid or liquid are dissolved in a volatile liquid.

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