Class 11th

14.39. What should be the tolerable limit of F ions in drinking water?

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1 ppm or 1 mg dm^-3.

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11 months ago

14.38. What are insecticides? Give examples of insecticides.

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A Toxic substance that is used to kill insects is called an insecticide. For example: DDT, BHC.

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14.7. List out the gases which are considered as major source of air pollution.

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Carbon monoxide (CO), sulphur dioxide (SO₂) and oxides of nitrogen (NO₂).

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14.35. Cite examples where green chemistry can be applied.

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Class 11th Classification of Elements and Periodicity in Prop

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Green chemistry can be applied as mentioned in the following examples:

(i) In dry-cleaning, the use of liquefied CO₂ in place of tetrachloroethene.

(ii) In the bleaching of paper using hydrogen peroxide instead of chlorine.

(iii) In the manufacture of chemicals like ethanol, using environment-friendly chemicals and conditions.

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3.36. The size of isoelectronic species-F^–, Ne and Na⁺ is affected by

(a) Nuclear charge (Z)

(b) Valence principal quantum number (n)

(c) Electron-electron interaction in the outer orbitals

(d) None of the factors because their size is the same

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Contributor-Level 10

3.36. (a) Nuclear charge (Z).

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14.34. What is the full form of PCBs and what are they?

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Class 11th Classification of Elements and Periodicity in Prop

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PCBs are polychlorinated biphenyls. They are contaminants of water. They are used as fluids in transformers and capacitors.

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3.35. Anything that influences the valence electrons will affect the chemistry of the element. Which one of the following factors does not affect the valence shell?

(a) Valence principal quantum number (n)

(b) Nuclear charge (Z)

(c) Nuclear mass

(d) Number of core electrons

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Class 11th Classification of Elements and Periodicity in Prop

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3.35. (c) Nuclear mass.

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3.34. Which of the following statements related to the modem periodic table is incorrect?

(a) The p-block has 6 columns, because a maximum of 6 electrons can occupy all the orbitals in a p-subshell.

(b) The d-block has 8 columns, because a maximum of 8 electrons can occupy all the orbitals in a d-subshell.

(c) Each block contains a number of columns equal to the number of electrons that can occupy that subshell.

(d) The block indicates value of azimuthal quantum number (l) for the last subshell that received electrons in building up the electronic configuration.

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3.34. Statement (b) is incorrect.

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Class 11th Classification of Elements and Periodicity in Prop

14.34. Ozone depletion is mainly due to

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11 months ago

3.33. In the modern periodic table, the period indicates the value of

(a) Atomic number

(b) Mass number

(c) Principal quantum number

(d) Azimuthal quantum number?

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