A) Tetrahedral
B) Linear
C) Trigonal planar
D) Octahedral
Correct Answer: A) Tetrahedral
Explanation: Methane, with the chemical formula CH₄, exhibits a tetrahedral shape. This geometry arises because the carbon atom forms four sigma bonds with hydrogen atoms, placing them at the maximum distance from each other to minimize repulsion, which results in a tetrahedral shape.
A) -1
B) -2
C) 0
D) +1
Correct Answer: B) -2
Explanation: In most of its compounds, oxygen exhibits an oxidation state of -2. This is a typical state for oxygen, reflecting its strong electronegativity and ability to gain electrons when forming compounds, except in peroxides where it has an oxidation state of -1 and in molecular oxygen (O₂) where it is 0.
A) Deposition
B) Sublimation
C) Condensation
D) Evaporation
Correct Answer: B) Sublimation
Explanation: Sublimation is the process by which a solid changes directly into a gas without first becoming a liquid. This phenomenon is observed in dry ice, which is solid carbon dioxide that sublimates at room temperature and pressure.
A) CaSO₄·2H₂O
B) CaCO₃
C) NaCl
D) Fe₂O₃
Correct Answer: A) CaSO₄·2H₂O
Explanation: Gypsum has the chemical formula CaSO₄·2H₂O. It is a hydrated calcium sulfate used widely in the construction industry for making plaster and drywall because of its ability to harden when mixed with water and then reheated.
A) Nitrogen
B) Oxygen
C) Carbon dioxide
D) Hydrogen
Correct Answer: C) Carbon dioxide
Explanation: Carbon dioxide (CO₂) is a major component of the atmospheres of Mars and Venus, comprising about 95% and 96%, respectively. In contrast, Earth’s atmosphere contains only about 0.04% carbon dioxide, with nitrogen and oxygen being the dominant gases.
A) Ductility
B) Malleability
C) Brittleness
D) Hardness
Correct Answer: A) Ductility
Explanation: Ductility is a property of metals that allows them to be stretched or drawn into wires without breaking. This property is crucial for applications in electrical wiring and the construction of metal frameworks.
A) Charles’s Law
B) Boyle’s Law
C) Avogadro’s Law
D) Dalton’s Law
Correct Answer: B) Boyle’s Law
Explanation: Boyle’s Law states that the pressure of a given mass of an ideal gas is inversely proportional to its volume when the temperature is kept constant. This fundamental principle of gas behavior is critical in various scientific calculations and engineering applications.
A) Carbon
B) Chromium
C) Zinc
D) Aluminum
Correct Answer: B) Chromium
Explanation: Chromium is added to steel to make stainless steel. The presence of at least 10.5% chromium in steel significantly enhances its corrosion resistance by forming a passive layer of chromium oxide on the surface, which prevents further surface corrosion and blocks corrosion from spreading into the metal’s internal structure.
A) Carbon-12
B) Carbon-13
C) Carbon-14
D) Carbon-15
Correct Answer: C) Carbon-14
Explanation: Carbon-14 is the isotope used in radiocarbon dating. It is a radioactive isotope of carbon with a half-life of about 5,730 years and is used to determine the age of organic materials up to about 50,000 years old.
A) Water
B) Hydrogen peroxide
C) Hydrochloric acid
D) Heavy water
Correct Answer: A) Water
Explanation: Dihydrogen monoxide is a less commonly used chemical name for water, which is H₂O. This compound is vital for all known forms of life and has unique properties that make it essential to many natural and technological processes.
A) Hydrochloric acid
B) Nitric acid
C) Sulfuric acid
D) Aqua regia
Correct Answer: D) Aqua regia
Explanation: Aqua regia, a mixture of nitric acid and hydrochloric acid in a 1:3 ratio, is known for its ability to dissolve gold and platinum. This capability is due to its highly corrosive nature and the effectiveness of the mixed acids at breaking down noble metals.
A) 0
B) 7
C) 14
D) 10
Correct Answer: B) 7
Explanation: A neutral solution has a pH of 7 at 25°C, indicating that the concentration of hydrogen ions is equal to the concentration of hydroxide ions, making it neither acidic nor basic.
A) Diamond
B) Quartz
C) Graphite
D) Silicon carbide
Correct Answer: A) Diamond
Explanation: Diamond is the hardest natural substance known on Earth. Its atomic structure makes it nearly impossible for most materials to scratch or damage it, which is why it’s also valued in industrial applications for cutting and grinding.
A) Oxygen
B) Helium
C) Hydrogen
D) Nitrogen
Correct Answer: C) Hydrogen
Explanation: Hydrogen is the most abundant gas in the Sun’s atmosphere. The Sun, like other stars, is primarily composed of hydrogen, which it uses in nuclear fusion processes to produce energy.
A) Mercury
B) Lead
C) Bromine
D) Iodine
Correct Answer: C) Bromine
Explanation: Bromine is one of the two elements that are liquids at room temperature, the other being mercury. Bromine is a reddish-brown liquid at room conditions.
A) Carbon dioxide
B) Methane
C) Nitrous oxide
D) Chlorofluorocarbons
Correct Answer: D) Chlorofluorocarbons
Explanation: Chlorofluorocarbons (CFCs) are chemicals that were widely used in refrigeration, air conditioning, and aerosol propellants. They are known to cause significant depletion of the stratospheric ozone layer, which protects Earth from harmful ultraviolet radiation.
A) Vitamin A
B) Vitamin B12
C) Vitamin D
D) Vitamin E
Correct Answer: C) Vitamin D
Explanation: Vitamin D is synthesized by the human body when it is exposed to sunlight, specifically ultraviolet B rays. This vitamin is crucial for the absorption of calcium and the promotion of bone health.
A) Oxygen
B) Water
C) Carbon dioxide
D) Both A and B
Correct Answer: D) Both A and B
Explanation: Rusting of iron occurs due to the presence of both oxygen and water. This oxidation-reduction reaction leads to the formation of iron oxides, commonly seen as rust.
A) Potassium nitrate
B) Sodium chloride
C) Magnesium sulfate
D) Calcium carbonate
Correct Answer: A) Potassium nitrate
Explanation: Potassium nitrate, commonly known as saltpeter, is used in fertilizers and as a component of gunpowder. It is also used in food preservation and as a meat curing agent.
A) Boyle’s Law
B) Charles’s Law
C) Avogadro’s Law
D) Gay-Lussac’s Law
Correct Answer: C) Avogadro’s Law
Explanation: Avogadro’s Law states that equal volumes of all gases, at the same temperature and pressure, contain the same number of molecules. This fundamental chemical law helps in understanding the relationships between volume and the amount of gas if temperature and pressure are constant.
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