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ScienceClass 10CBSE

Explain the concept of 'accumulation of variations' in sexually reproducing organisms. How does this differ from variations observed in asexually reproducing organisms?

In sexually reproducing organisms, variations accumulate over generations due to the shuffling of genes during meiosis and fertilization. Each parent contributes a unique set of genes, and the combination of these genes in the offspring creates new variations. This continuous mixing leads to a wider range of phenotypic differences within a population. In contrast, asexually reproducing organisms produce offspring that are genetically identical to the parent (clones), with variations arising primarily from random mutations. Therefore, the accumulation of variations is much slower and less diverse in asexual reproduction compared to sexual reproduction.

ScienceClass 10CBSE

Explain why generally metals are solid at room temperature, but mercury is a liquid.

Most metals are solid at room temperature because their constituent atoms are held together by strong metallic bonds. These bonds require a significant amount of energy to break, leading to high melting points. Mercury (Hg) is an exception; it is a liquid at room temperature. This is due to its unique electronic configuration and relativistic effects, which lead to weaker metallic bonding compared to other metals. The electrons in mercury are more tightly bound to their nuclei, making them less available for forming strong metallic bonds across the entire structure, resulting in a lower melting point.

ScienceClass 10CBSE

What is the role of a flux in the metallurgical process?

In metallurgy, a flux is a substance added to the ore during smelting to remove impurities (gangue) from the molten metal. The flux reacts with the non-fusible impurities to form a fusible product called slag, which is lighter than the molten metal and floats on its surface, making it easy to separate. For example, in the extraction of iron, limestone (CaCO3) is used as a flux. It decomposes to CaO, which then reacts with silica (SiO2, an acidic impurity) to form calcium silicate (CaSiO3) slag.

ScienceClass 10CBSE

Why are certain metals like copper and aluminium used for making electrical wires, while iron is not?

Copper and aluminium are excellent conductors of electricity, second only to silver, and they are also ductile, allowing them to be drawn into thin wires. They are relatively inexpensive compared to silver and offer a good balance of conductivity, ductility, and cost-effectiveness. Iron, while a metal, is not as good a conductor as copper or aluminium, and it is also more prone to rusting and is less ductile, making it unsuitable for drawing into efficient and durable electrical wires.

ScienceClass 10CBSE

Why is it important to remove the protective oxide layer from magnesium ribbon before burning it?

Magnesium is a reactive metal and readily reacts with oxygen in the air to form a thin, dull, and stable layer of magnesium oxide (MgO) on its surface. This oxide layer acts as a protective barrier, preventing further reaction of the magnesium with oxygen. If this layer is not removed (e.g., by rubbing with sandpaper) before burning, it will hinder the combustion process, making it difficult for the magnesium to ignite and burn brightly.

ScienceClass 10CBSE

Explain the term 'amalgam'. Give an example of its use.

An amalgam is an alloy of mercury with one or more other metals. Mercury is liquid at room temperature, and when it mixes with other metals, it forms a solid or liquid alloy. A common example of its use is in dental fillings, where silver amalgam (an alloy of mercury, silver, tin, and copper) was traditionally used to fill cavities due to its malleability when wet and hardness when set.

ScienceClass 10CBSE

What happens when a reactive metal reacts with a non-metal? Illustrate with an example.

When a reactive metal reacts with a non-metal, they typically form an ionic compound. The metal atom readily loses its valence electrons to become a positively charged ion (cation), and the non-metal atom gains these electrons to become a negatively charged ion (anion). These oppositely charged ions are then held together by strong electrostatic forces of attraction, forming an ionic bond. Example: Reaction between Magnesium (metal) and Oxygen (non-metal). Magnesium loses two electrons to form Mg2+, and oxygen gains two electrons to form O2-. They combine to form Magnesium Oxide (MgO). 2Mg(s) + O2(g) → 2MgO(s)

ScienceClass 10CBSE

Why is graphite, a non-metal, a good conductor of electricity?

Graphite is an allotrope of carbon, a non-metal. Its unique structure consists of layers of carbon atoms arranged in hexagonal rings. Within each layer, carbon atoms are covalently bonded, but each carbon atom is bonded to only three other carbon atoms, leaving one valence electron free. These delocalized electrons between the layers are free to move, making graphite an excellent conductor of electricity, unlike most other non-metals.

ScienceClass 10CBSE

Explain why noble metals like gold and platinum are found in a free state in nature, while most other metals are found in combined states.

Noble metals like gold and platinum are at the very bottom of the reactivity series. They are highly unreactive and do not readily combine with other elements like oxygen, water, or acids present in the environment. Due to their low reactivity, they exist as free elements (native state) in the Earth's crust. Most other metals are more reactive and readily form compounds with other elements, hence found in combined states as ores.

ScienceClass 10CBSE

What is an alloy? Give two reasons why alloys are preferred over pure metals for certain applications.

An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal. Alloys are preferred over pure metals for certain applications because: 1. They often have improved properties, such as increased hardness, strength, or corrosion resistance, compared to their constituent pure metals. 2. Their melting points can be lowered, making them easier to cast or work with. For example, stainless steel (an alloy of iron, chromium, and nickel) is much more resistant to rust than pure iron.

ScienceClass 10CBSE

Describe the process of anodising. What is its purpose?

Anodising is an electrolytic process used to increase the thickness of the natural oxide layer on the surface of metal parts, typically aluminium. The aluminium article is made the anode and dipped in an electrolyte like dilute sulphuric acid. When current is passed, oxygen gas is evolved at the anode, which reacts with aluminium to form a thicker, stronger, and more corrosion-resistant aluminium oxide layer. The purpose of anodising is to protect the metal from corrosion, improve its wear resistance, and allow for decorative colouring.

ScienceClass 10CBSE

Why are non-metals generally poor conductors of electricity, while metals are good conductors?

Metals have a 'sea' of delocalized electrons that are free to move throughout the metallic lattice. These free electrons are responsible for conducting electricity. Non-metals, on the other hand, typically hold their electrons tightly in covalent bonds or have a complete outer shell, meaning they do not have free electrons to carry an electric current, making them poor conductors. Graphite is an exception among non-metals due to its unique layered structure with delocalized electrons.

ScienceClass 10CBSE

Explain the concept of thermite reaction. Where is it primarily used?

The thermite reaction is a highly exothermic redox reaction between a metal oxide and a more reactive metal (usually aluminium) powder. In this reaction, aluminium reduces the metal oxide to its molten metal state, generating a large amount of heat. A common example is the reaction between iron(III) oxide and aluminium: Fe2O3(s) + 2Al(s) → 2Fe(l) + Al2O3(s) + Heat. It is primarily used for welding railway tracks and cracked machine parts due to the high temperature produced and the molten iron formed.

ScienceClass 10CBSE

What are amphoteric oxides? Give an example and write balanced chemical equations for its reaction with both an acid and a base.

Amphoteric oxides are metal oxides that react with both acids and bases to produce salt and water. An example is aluminium oxide (Al2O3). Reaction with acid: Al2O3(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2O(l) Reaction with base: Al2O3(s) + 2NaOH(aq) → 2NaAlO2(aq) + H2O(l) (or 2NaOH(aq) + Al2O3(s) + 3H2O(l) → 2Na[Al(OH)4](aq) depending on the form of sodium aluminate)

ScienceClass 10CBSE

Explain why sodium metal is stored under kerosene oil.

Sodium is a highly reactive metal. It reacts vigorously with oxygen and moisture present in the air, sometimes even catching fire. To prevent this reaction and ensure its safe storage, sodium metal is kept immersed in kerosene oil, which is unreactive with sodium and prevents its contact with air and water.

ScienceClass 10CBSE

Why do metals generally form positive ions (cations), while non-metals generally form negative ions (anions)?

Metals typically have 1, 2, or 3 electrons in their outermost shell. They tend to lose these valence electrons to achieve a stable noble gas configuration, forming positively charged ions (cations). Non-metals, on the other hand, usually have 4 to 7 electrons in their outermost shell. They tend to gain electrons to complete their octet and achieve a stable noble gas configuration, forming negatively charged ions (anions).

ScienceClass 10CBSE

Differentiate between malleability and ductility, providing an example of a metal that exhibits both properties prominently.

Malleability is the property of a material to be hammered or pressed into thin sheets without breaking. Ductility is the property of a material to be drawn into thin wires without breaking. Gold is an excellent example of a metal that exhibits both malleability and ductility prominently, allowing it to be beaten into extremely thin foils and drawn into fine wires.

ScienceClass 10CBSE

What is corrosion? Explain the conditions necessary for the rusting of iron and suggest two methods to prevent it.

Corrosion is the gradual deterioration of a material, usually a metal, by chemical reaction with its environment. Rusting is a specific type of corrosion that affects iron and its alloys. The conditions necessary for rusting of iron are the presence of both oxygen (from air) and water (moisture). Two methods to prevent rusting include painting (which creates a barrier between the iron and the environment) and galvanization (coating iron with a layer of zinc, which acts as a sacrificial metal).

ScienceClass 10CBSE

Describe the process of extracting metals from their ores, specifically focusing on the steps involved for moderately reactive metals.

Moderately reactive metals like zinc, iron, and lead are usually found as sulphides or carbonates in their ores. The extraction process typically involves: 1. Concentration of the ore. 2. Conversion of sulphide ores to oxides by roasting (heating in air). 3. Conversion of carbonate ores to oxides by calcination (heating in limited air). 4. Reduction of the metal oxides to the metal using a reducing agent like carbon. For example, ZnO + C → Zn + CO.

ScienceClass 10CBSE

What are ionic compounds? Explain their formation with a suitable example.

Ionic compounds are chemical compounds formed by the electrostatic attraction between oppositely charged ions. They are typically formed between a metal and a non-metal, where the metal atom loses electrons to form a positive ion (cation) and the non-metal atom gains electrons to form a negative ion (anion). For example, in the formation of sodium chloride (NaCl), sodium (Na) loses one electron to become Na+, and chlorine (Cl) gains one electron to become Cl-. The electrostatic attraction between Na+ and Cl- forms the ionic bond.

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