iGCSE Chemistry (0620) Theory (Core):2.1 Elements, compounds and mixtures: Exam Style Questions Paper 3- New Syllabus

(a)
For the correct answer:
nitrogen

Nitrogen is in Group V of the Periodic Table, meaning it has 5 electrons in its outer shell. To achieve a full outer shell (8 electrons, like the noble gas neon), it gains 3 electrons. This gain of 3 electrons forms the nitride ion, $\mathrm{N}^{3-}$, which carries a 3- charge. The other elements in the list either form positive ions (metals), do not form ions (noble gases), or form anions with different charges (e.g., chlorine forms $\mathrm{Cl}^{-}$, oxygen forms $\mathrm{O}^{2-}$).

(b)
For the correct answer:
copper or gold

Transition elements are located in the central block of the Periodic Table (between Groups II and III). They are characteristically metals with high densities, high melting points, and they form coloured compounds. Both copper (Cu) and gold (Au) fit this description perfectly. Copper forms blue compounds, while gold is known for its distinctive yellow colour and very low reactivity.

(c)
For the correct answer:
carbon dioxide

The standard chemical test for carbon dioxide ($\mathrm{CO}_2$) is to bubble the gas through limewater, which is a solution of calcium hydroxide, $\mathrm{Ca(OH)_2}$. If carbon dioxide is present, it reacts to form a white precipitate of calcium carbonate ($\mathrm{CaCO_3}$), making the limewater turn milky or cloudy. This is a specific and confirmatory test.

(d)
For the correct answer:
nitrogen

Clean, dry air is a mixture of gases. By volume, its approximate composition is $78\%$ nitrogen ($\mathrm{N_2}$), $21\%$ oxygen ($\mathrm{O_2}$), and about $1\%$ other gases, which include argon, carbon dioxide, and traces of noble gases. Nitrogen is therefore the most abundant gas in the atmosphere.

(e)
For the correct answer:
copper

Copper is the standard metal for electrical wiring. This is primarily due to two of its physical properties: its excellent electrical conductivity, which allows electricity to flow with minimal energy loss, and its high ductility, which allows it to be drawn into thin, flexible wires without breaking.

(f)
For the correct answer:
gold

The reactivity series orders metals by their tendency to react. Gold is famously unreactive and is found native (as a pure element) in the Earth’s crust. It is positioned very low in the reactivity series, below copper and silver, meaning it resists corrosion and does not react with dilute acids. Therefore, from the list, it is the least reactive metal.

(g)
For the correct answer:
iodine

A diatomic molecule consists of two atoms bonded together. In the list, chlorine, iodine, nitrogen, and oxygen are diatomic ($\mathrm{Cl_2, I_2, N_2, O_2}$). At room temperature and pressure (r.t.p.), chlorine is a gas, nitrogen is a gas, and oxygen is a gas. Iodine ($\mathrm{I_2}$) is the only one that exists as a grey-black solid with a slight metallic lustre.

(h)
For the correct answer:
calcium oxide

In the extraction of iron in a blast furnace, limestone ($\mathrm{CaCO_3}$) is added. It thermally decomposes to form calcium oxide ($\mathrm{CaO}$) and carbon dioxide. The calcium oxide is a basic oxide that reacts with acidic sandy impurities, mainly silicon dioxide ($\mathrm{SiO_2}$), to form calcium silicate ($\mathrm{CaSiO_3}$). This molten waste product is called slag, which can be tapped off and used for road building.

(i)
For the correct answer:
carbon

The relative atomic mass ($A_r$) of an element is the weighted average mass of its isotopes compared to $\frac{1}{12}$th the mass of a carbon-12 atom. By definition, the $A_r$ of carbon is exactly $12.0$. This is a fundamental standard in chemistry.