Question Discussion & Solution

Pages are necessary part of book. Book can be fiction or non-fiction. Pictures are not always necessary and not all books have learning. So, all other options are not necessary except Pages.

The correct answer is Barium.

Key Points

• Metal salts commonly used in firework displays include calcium chloride, sodium nitrate, barium chloride, copper chloride, etc.
• The green flame produced in fireworks is due to the presence of Barium.
• The blue flame is due to the presence of Copper.
• The orange flame is due to the presence of Calcium.
• A yellow flame is due to the presence of Sodium.
• Lithium is used to impart a red colour to fireworks.

Additional Information

• Barium (Ba):
  • The atomic number is 56.
  • It is mostly used in drilling fluids for oil and gas wells and also used in paints and glassmaking.
  • It is found in combination with other elements.
  • Barite is one of the major ores of Barium.
• Calcium (Ca):
  • The atomic number is 20.
  • Calcium provides strength to bones and teeth along with vitamins.
  • It also plays an important role in blood formation, muscle contraction, clotting of blood, etc.
  • Milk, eggs, fish, etc. are the main sources of calcium.
• Lithium (Li):
  • Atomic Number is 3.
  • Lithium is the lightest metal on the periodic table.
  • It is widely used in rechargeable batteries for mobile phones, laptops, digital cameras, etc.
• Chromium (Cr):
  • The atomic number is 24.
  • It is used in manufacturing stainless steel.
  • Chromite is the major ore of Chromium.
  • It is a blue-white hard, brittle, and very corrosion-resistant metal and is used to produce several alloys.

The correct answer is Total Internal Reflection of Light.

Key Points

• Total Internal Reflection of Light
  • When a light ray, traveling from a denser medium towards a rarer medium is incident at the interface at an angle of incidence greater than the critical angle, then the rays are reflected back into the denser medium.
  • Practical Applications of Total Internal Reflection
  1. The working of optical fiber is based on total internal reflection.
  2. Mirage is formed due to total internal reflection.
  3. The brilliance of diamonds is mainly due to the total internal reflection of light inside them.

Additional Information

• Reflection of Light
  • The phenomenon of rebounding back of light rays in the same medium on striking a smooth surface is called reflection of light.
  • Silver metal is one of the best reflectors of light.
• Diffraction of Light
  • The phenomenon of bending of light around the corners and the spreading of light within the geometrical shadow of the opaque obstacles is called diffraction of light.
• Refraction of Light
  • Change in the path of a light ray as it passes from one medium to another is called refraction.

Given: Girl, Boy, Human

All human are boy and girl.

Water Pollution:

• Water pollution occurs when harmful substances often chemicals or microorganisms contaminate a stream, river, lake, ocean, aquifer, or other body of water, degrading water quality and rendering it toxic to humans or the environment.
• Water pollution is a major environmental issue in India.
• The largest source of water pollution in India is untreated sewage.
• Other sources of pollution include agricultural runoff and unregulated small-scale industry.
• Most rivers, lakes, and surface water in India are polluted due to industries, untreated sewage, and solid wastes.

Hence, option 1 is the correct answer. 

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​Untreated Sewage

• A 2007 study found that the discharge of untreated sewage is the single most important source of pollution of surface and groundwater in India.
• There is a large gap between the generation and treatment of domestic wastewater in India.
• The problem is not only that India lacks sufficient treatment capacity but also that the sewage treatment plants that exist do not operate and are not maintained.

1. Agriculture run-off: Farms discharge large quantities of agrochemicals, organic matter, drug residues, sediments, and saline drainage into water bodies. Nevertheless, agricultural pollution, aggravated by increased sediment runoff and groundwater salinization, is also becoming an issue.
2. Unregulated small-scale industries and religious practices comparatively have less contribution to water pollution in major rivers of India.