General Science

Concept: Quick lime is a common chemical compound with a specific chemical formula. Knowing the formula allows us to identify the constituent elements. Step 1: Identify the chemical name and formula of Quick Lime Quick lime is the common name for Calcium Oxide. The chemical formula for Calcium Oxide is CaO. Step 2: Identify the elements from the chemical formula The formula CaO indicates that one molecule of quick lime contains:
One atom of Calcium (symbol: Ca)
One atom of Oxygen (symbol: O) Step 3: Match the elements with the given list The given list of elements is: % Option (i) Ca (Calcium) % Option (ii) H (Hydrogen) % Option (iii) O (Oxygen) % Option (iv) C (Carbon) From our analysis, quick lime (CaO) contains Calcium (Ca) and Oxygen (O). So, elements (i) Ca and (iii) O are present in quick lime. Step 4: Choose the correct option Option (1) (i), (ii) and (iii) includes Hydrogen (H), which is not in CaO. Option (2) (i), (iii) and (iv) includes Carbon (C), which is not in CaO. Option (3) (i) and (iii) correctly lists Calcium (Ca) and Oxygen (O). Option (4) (i), (ii), (iii) and (iv) includes Hydrogen (H) and Carbon (C), which are not in CaO. Therefore, the elements present in quick lime are Calcium (Ca) and Oxygen (O).

Concept: Ores are naturally occurring rocks or minerals from which metals can be extracted economically. Calamine is a historical name for an ore. Step 1: Identifying Calamine Calamine is an ore that is primarily composed of zinc carbonate ( ). The mineral name for zinc carbonate is smithsonite. Historically, "calamine" has also sometimes referred to hydrated zinc silicate (hemimorphite), but it is most commonly associated with zinc carbonate. In either case, it is an ore of zinc. Step 2: Determining the metal obtained from Calamine Since calamine is mainly zinc carbonate ( ), the metal that can be extracted from it is Zinc (Zn). Step 3: Analyzing the options % Option (M) (1) Ca (Calcium): Ores of calcium include limestone ( ), gypsum ( ). % Option (N) (2) Zn (Zinc): Calamine ( ) is an ore of zinc. Other zinc ores include sphalerite/zinc blende (ZnS) and zincite (ZnO). % Option (O) (3) Mg (Magnesium): Ores of magnesium include magnesite ( ), dolomite ( ), carnallite. % Option (P) (4) Hg (Mercury): The principal ore of mercury is cinnabar (HgS). Therefore, calamine is an ore of zinc. (Calamine lotion, known for its soothing properties, also contains zinc oxide or zinc carbonate).

Concept: Earth's atmosphere is a mixture of several gases. The relative amounts of these gases determine which one is the most abundant. Step 1: Composition of Earth's Dry Atmosphere (Approximate Percentages by Volume)
Nitrogen ( ): About 78.08%
Oxygen ( ): About 20.95%
Argon (Ar): About 0.93%
Carbon Dioxide ( ): About 0.04% (variable, but this is a typical current value)
Other gases (Neon, Helium, Methane ( ), Krypton, Hydrogen, etc.): Trace amounts, collectively less than 0.01%. Water vapor is also a significant component of the atmosphere, but its concentration is highly variable (0-4%). The question usually refers to the composition of dry air. Step 2: Identifying the most abundant gas From the percentages, Nitrogen ( ) is clearly the most abundant gas, making up roughly 78% of the Earth's atmosphere. Oxygen ( ) is the second most abundant. Step 3: Evaluating the options
(1) (Carbon Dioxide): Present in a small percentage ( ).
(2) (Oxygen): Second most abundant ( ).
(3) (Methane): Present in trace amounts (parts per million).
(4) (Nitrogen): Most abundant ( ). Therefore, Nitrogen ( ) is the most abundant gas in Earth's atmosphere.

Concept: Metals are found in the Earth's crust either in their native (free) state or in combined states as minerals (ores). The tendency to be found in a free state depends on their chemical reactivity. Less reactive metals are more likely to be found in their free state. Step 1: Understanding "Free State" "Free state" or "native state" means the metal exists in its elemental form, uncombined with other elements. This is characteristic of metals that are low in the reactivity series (also known as the activity series). Step 2: Reactivity of Metals
Highly Reactive Metals (e.g., K, Na, Ca, Mg, Al): Found only in combined states (ores).
Moderately Reactive Metals (e.g., Zn, Fe, Pb, Cu): Mostly found in combined states, but copper (Cu) can sometimes be found in its native state.
Least Reactive Metals (e.g., Ag, Au, Pt): These are often called "noble metals" due to their low reactivity. They are commonly found in their free state. Step 3: Analyzing the options Let's check the reactivity of the metals in each set:
(1) Al, Cu, Ag:
Aluminium (Al): Highly reactive, found as bauxite ore ( ). Not in free state.
Copper (Cu): Moderately reactive, mostly as ores (e.g., chalcopyrite), but native copper exists.
Silver (Ag): Low reactivity, often found in free state. This set is not entirely free state metals due to Al.
(2) Au, Fe, Ag:
Gold (Au): Very low reactivity, found in free state.
Iron (Fe): Moderately reactive, found as ores (e.g., hematite, magnetite). Not typically in free state (except meteoritic iron).
Silver (Ag): Low reactivity, often found in free state. This set is not entirely free state metals due to Fe.
(3) Cu, Au, Fe:
Copper (Cu): Can be found in free state.
Gold (Au): Found in free state.
Iron (Fe): Not typically in free state. This set is not entirely free state metals due to Fe.
(4) Ag, Au, Pt:
Silver (Ag): Low reactivity, found in free state.
Gold (Au): Very low reactivity, found in free state.
Platinum (Pt): Very low reactivity, found in free state. All three metals in this set are known to be found in their free (native) state due to their low chemical reactivity. Therefore, the set Ag, Au, Pt consists of three metals commonly found in their free state.

Concept: Coal mines can contain flammable gases trapped within the coal seams. When these gases mix with air in certain proportions, they can form explosive mixtures. Step 1: Gases found in Coal Mines Coal formation processes can trap various gases. The most significant flammable gas found in coal mines is Methane ( ). Methane is the main component of natural gas. In coal mines, methane is often referred to as "firedamp." Another major hazard is coal dust itself, which can also be explosive when suspended in air in sufficient concentrations. Step 2: Conditions for Explosion For a gas to cause an explosion, it must be: % Option (A) Flammable (able to burn). % Option (B) Mixed with an oxidizer (usually oxygen from the air) in proportions that fall within its explosive or flammability limits. % Option (C) Ignited by a source of ignition (like a spark, open flame, or hot surface). Step 3: Analyzing the options % Option (D) (1) Methane ( ): Methane is highly flammable and forms explosive mixtures with air. It is a well-known and primary cause of explosions in coal mines (firedamp explosions). % Option (E) (2) Ethane ( ): Ethane is also a flammable gas and can be present with methane, but methane is typically the predominant flammable gas associated with coal mine explosions. % Option (F) (3) Nitrogen ( ): Nitrogen is an inert gas; it does not burn and is not explosive. It's the main component of air. % Option (G) (4) Oxygen ( ): Oxygen is necessary for combustion (it's an oxidizer), but oxygen itself is not flammable or explosive. It supports the combustion of flammable substances. The image indicates this option was circled, which is incorrect as oxygen supports combustion but isn't the fuel itself for an explosion in this context. Step 4: Identifying the primary cause of explosions Methane ( ) is the gas most notorious for causing explosions in coal mines. When mixed with air (which contains oxygen) in concentrations roughly between 5% and 15% methane, it can be ignited and explode violently.

Concept: Gels are a type of colloid. A colloid is a mixture in which one substance of microscopically dispersed insoluble particles is suspended throughout another substance. The type of colloid is defined by the phases of the dispersed substance and the dispersion medium. Step 1: Understanding what a gel is A gel is a colloidal system in which a liquid (the dispersed phase) is dispersed throughout a solid continuous network (the dispersion medium). The solid network gives the gel its structure and semi-solid, jelly-like consistency, trapping the liquid within it. Step 2: Analyzing the options for colloidal systems
(1) liquid in a solid: This describes a gel. The liquid particles are dispersed in a solid medium. Examples: gelatin, jelly, cheese, butter, gel toothpaste.
(2) solid in a gas: This describes a solid aerosol. Examples: smoke, dust in the air.
(3) liquid in liquid: This describes an emulsion. Examples: milk, mayonnaise.
(4) gas in solid: This describes a solid foam or solid sol. Examples: pumice stone, styrofoam, bread. Step 3: Applying to gel toothpaste Gel toothpaste has a characteristic jelly-like, semi-solid texture. This structure is formed by a solid network (gelling agents like hydrated silica or polymers) that entraps liquid components (like water, sorbitol, glycerin). Therefore, a gel toothpaste is a system where a liquid is dispersed in a solid.

Concept: The cooling effect observed in water stored in earthen pots (like a matka or surahi) is due to a specific phase change process that requires energy. Step 1: Properties of an earthen pot Earthen pots are porous, meaning they have very tiny, microscopic pores or holes in their walls. Step 2: The process occurring Water kept inside the earthen pot seeps out through these tiny pores to the outer surface of the pot. On the outer surface, this water comes into contact with the surrounding air. The water on the outer surface undergoes evaporation. Evaporation is the process where a liquid changes into its vapor (gas) phase at a temperature below its boiling point. Step 3: How evaporation causes cooling Evaporation is an endothermic process, meaning it requires energy (heat). The molecules of water that evaporate from the surface take this energy (latent heat of vaporization) from:
The remaining water on the surface of the pot.
The pot itself.
Ultimately, from the water inside the pot. As this heat energy is continuously removed from the system (pot and water inside) to fuel the evaporation, the temperature of the water inside the pot decreases, making it cool. Step 4: Analyzing other options
(1) Diffusion: The movement of particles from an area of higher concentration to lower concentration. While involved in vapor movement, it's not the primary cooling mechanism.
(2) Transpiration: The process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers. Not relevant to an earthen pot.
(3) Osmosis: The movement of solvent (like water) across a semipermeable membrane from a region of low solute concentration to high solute concentration. Not the primary cooling mechanism here. The cooling is directly caused by the energy absorbed during evaporation.

Concept: Chemical symbols are abbreviations used in chemistry for chemical elements. Each element has a unique one- or two-letter symbol. Some symbols are derived from the element's Latin name. Step 1: Understanding Chemical Symbols Chemical symbols are internationally recognized codes for elements. The first letter is always capitalized, and if there's a second letter, it's lowercase. Step 2: Identifying the symbol for Tin The chemical symbol for tin is Sn. This symbol comes from its Latin name, "stannum." Step 3: Analyzing the options and identifying other elements
(1) Ti: This is the chemical symbol for Titanium.
(2) Sb: This is the chemical symbol for Antimony (from its Latin name "stibium").
(3) Sn: This is the chemical symbol for Tin (from its Latin name "stannum").
(4) Te: This is the chemical symbol for Tellurium. Therefore, the correct chemical symbol for tin is Sn.

Concept: Sublimation is a process where a substance transitions directly from the solid phase to the gas phase without passing through the liquid phase. This property can be used for purification if one component of a mixture sublimes while others do not. Step 1: Understanding Sublimation for Purification If a mixture contains a sublimable substance (one that can sublime) and non-sublimable impurities, heating the mixture will cause the sublimable substance to turn into vapor. This vapor can then be cooled and condensed back into a solid in a separate location, leaving the impurities behind. Step 2: Identifying substances that sublime Common substances that readily sublime at or near atmospheric pressure include:
Iodine
Naphthalene (mothballs)
Camphor
Dry ice (solid Carbon Dioxide)
Ammonium Chloride ( ) Step 3: Analyzing the options
(1) Ammonium Chloride ( ): This is a well-known example of a compound that sublimes upon heating. It transitions directly from solid to gas and can be condensed back to solid.
(2) Calcium Carbonate ( ): Also known as limestone or chalk. It does not sublime under normal heating conditions; instead, it decomposes at high temperatures (e.g., ) into calcium oxide and carbon dioxide.
(3) Sodium Carbonate ( ): Also known as washing soda. It is a stable ionic solid that melts at a high temperature ( ) but does not typically sublime.
(4) Aluminium Chloride ( ): Anhydrous aluminium chloride is a covalent compound that sublimes at around . This is also a substance that can be purified by sublimation. However, ammonium chloride is a more common textbook example for sublimation at a simpler level. Given that Ammonium Chloride is listed and is a classic example, it is the intended answer. If both were present and only one could be chosen, context or common knowledge emphasis would guide. Step 4: Conclusion Among the given options, Ammonium Chloride is a classic example of a compound that can be purified by sublimation. Aluminium Chloride also sublimes, but Ammonium Chloride is a very standard example in introductory chemistry.