A: The copper coin is a metal (lustrous, malleable, good conductor). Sulfur is a non‑metal (dull, brittle, poor conductor). A distinguishing property is electrical conductivity: copper conducts electricity well; sulfur does not.

A: Zinc will react with dilute HCl producing effervescence (H₂ gas) and dissolve to form zinc chloride. Iron will react slowly producing hydrogen and iron chloride. Copper, being less reactive, will not react with dilute HCl under normal conditions, so no hydrogen gas will be observed.

A: Nail A (in wet sand) will rust faster because water (moisture) and oxygen are required for rusting. Wet sand retains moisture and provides the electrolyte necessary for corrosion, increasing rust formation.

A: Sodium is highly reactive with oxygen and moisture; if exposed to air it would oxidise rapidly and may react vigorously with moisture producing sodium hydroxide and hydrogen gas (which can ignite). Storing under oil prevents contact with air and water, keeping it safe.

A: Painting forms a barrier preventing oxygen and water from reaching the iron surface, halting further rusting. Removing loose rust is important because paint will not adhere well to flaky rust; removing it exposes a stable surface so the protective coating can bond and be effective.

A: Copper is a metal with free electrons that allow electric current to flow, so it conducts and lights the bulb. Plastic is a non‑metallic insulator; when the plastic coating is intact it prevents electrical contact, so the circuit is open and the bulb does not light.

A: Magnesium ribbon burns with a bright white flame producing white magnesium oxide; sulfur burns with a blue flame producing sulfur dioxide gas (pungent smell). Magnesium is a metal that readily oxidises producing a basic oxide, while sulfur is a non‑metal producing an acidic oxide.

A: Tarnish on brass (copper + zinc) is due to corrosion from moisture, oxygen and salts in the sea air forming copper salts (green patina). Minimisation: keep utensils dry, clean regularly, apply a protective coating (varnish) or store indoors away from salty air.

A: In copper sulfate, iron will displace copper because iron is more reactive than copper: Fe + CuSO₄ → FeSO₄ + Cu (orange/brown copper deposits). In zinc sulfate, iron may not displace zinc because iron is less reactive than zinc, so no reaction occurs. Displacement occurs when a more reactive metal displaces a less reactive one from its salt solution.

A: Aluminium forms a thin, protective layer of aluminium oxide on exposure to air which prevents further corrosion (passivation), causing a dull appearance but not structural damage. Iron forms hydrated iron oxides (rust) which are flaky and do not protect the metal, leading to continued corrosion. Thus aluminium resists extensive corrosion unlike iron.

A: This is galvanisation (zinc coating). Zinc acts as a sacrificial anode; it corrodes preferentially protecting the iron. Even if the coating is scratched, zinc near the exposed area still corrodes and prevents iron from rusting, offering continued protection.

A: Gold is a very unreactive metal (noble metal) and does not react with air or water, so it does not corrode easily and can be stored openly. Iron is reactive and prone to rusting; oiling provides a moisture barrier to prevent rust, hence iron tools are oiled and stored carefully.

A: Diamond is extremely hard and an electrical insulator because each carbon atom is bonded tetrahedrally, forming a rigid 3D network. Graphite is soft, slippery and conducts electricity because carbon atoms form layered structures with delocalised electrons in each layer. Different bonding arrangements (allotropes) lead to different properties despite the same element.

A: Steel is strong, tough and cost‑effective but heavier and prone to rust (requires protection). Aluminium alloy is lighter and resists corrosion better (forms oxide layer) leading to fuel efficiency, but it is more expensive and may be less strong for the same thickness. Choice depends on priorities: load capacity vs weight and corrosion resistance.

A: Metals that displace hydrogen from acids (like zinc or magnesium) liberate H₂ gas. Copper does not displace hydrogen from dilute acids. With nitric acid (an oxidising acid), copper reacts differently producing copper salts and nitrogen oxides, not hydrogen gas. The nature of the acid and the metal's reactivity determine products.

A: Sea air contains salt (sodium chloride) which forms electrolytes with moisture, accelerating electron transfer and corrosion. Higher humidity also promotes rusting. Protection: regular cleaning, coating with paint or oil, galvanisation or using stainless steel tools designed to resist corrosion in salty environments.

A: Combining methods gives multiple layers of protection: polymer coating prevents direct moisture contact; galvanisation provides sacrificial protection at exposed points. If the polymer is damaged, the zinc layer still protects. Using both increases longevity and reduces maintenance costs by offering redundant protection systems.

A: Aluminium forms a thin, tightly adherent oxide layer (Al₂O₃) that protects the metal from further oxidation (passivation). This layer prevents widespread corrosion, so aluminium appears not to rust. Under certain conditions (e.g., in presence of strong alkalis or salts and galvanic coupling), aluminium can corrode, but typical household exposure does not cause rust-like corrosion.

A: Iron will corrode and form rust in salty water. Stainless steel will resist rusting because chromium in the alloy forms a protective chromium oxide layer that prevents further oxidation. Stainless steel's corrosion resistance makes it suitable for such environments.

A: Recycling aluminium requires far less energy than extracting aluminium from bauxite (saving up to 90% of energy), reduces mining and environmental damage, conserves natural resources, lowers greenhouse gas emissions and reduces landfill waste. It is economically and environmentally beneficial and supports a circular economy.