p-Block Elements (Groups 15 to 18) - Practice Questions with Answers

Q1.

Which Group 15 element forms the diatomic gas that makes up 78% of air?

• A Nitrogen (N₂)
• B Oxygen
• C Phosphorus
• D Arsenic

Q2.

Which element in Group 16 is essential for cellular respiration?

• A Oxygen
• B Sulfur
• C Selenium
• D Tellurium

Q3.

Chlorine belongs to which group?

• A Group 17
• B Group 16
• C Group 18
• D Group 15

Q4.

Which p-block element is a liquid at room temperature?

• A Bromine (Br₂)
• B Chlorine
• C Iodine
• D Fluorine

Q5.

Which compound is responsible for the depletion of the ozone layer?

• A CFCs (chlorofluorocarbons)
• B CO₂, the greenhouse gas mainly linked to global warming
• C SO₂, the gas primarily responsible for acid rain formation
• D NO₂, the brownish gas contributing to photochemical smog

Q6.

Which form of phosphorus is most reactive?

• A White phosphorus (P₄)
• B Red phosphorus
• C Black phosphorus
• D Violet phosphorus

Q7.

Sulfuric acid (H₂SO₄) is produced industrially by:

• A Contact process
• B Haber process
• C Solvay process
• D Frasch process

Q8.

The most electronegative element in the p-block is:

• A Fluorine (F)
• B Chlorine (Cl)
• C Oxygen (O)
• D Nitrogen (N)

Q9.

Silicon is to electronics what __ is to life:

• A Carbon
• B Nitrogen
• C Oxygen
• D Phosphorus

Q10.

Helium, neon, argon, krypton, xenon, and radon belong to which group?

• A Group 18 (noble gases)
• B Group 17 in many documented cases
• C Group 16 according to conventional understanding
• D Group 1 in routine practice

Q11.

Which element is used in semiconductors and solar cells?

• A Silicon
• B Sulfur
• C Selenium
• D Bromine

Q12.

Which gas is used in neon signs?

• A Neon
• B Argon
• C Krypton
• D Xenon

Q13.

Which allotrope of carbon is the hardest natural substance?

• A Diamond
• B Graphite
• C Fullerene
• D Carbon black

Q14.

Nitrogen gas is unreactive (inert) mainly because:

• A N≡N triple bond has very high bond dissociation energy (945 kJ/mol)
• B N₂ molecules contain no valence electrons available for bonding
• C Nitrogen atoms have an unusually large atomic radius for their period
• D N₂ is technically classified as a noble gas

Q15.

Which acid is called 'oil of vitriol'?

• A Concentrated H₂SO₄
• B HNO₃ in general practice
• C HCl as frequently described
• D H₃PO₄ in most textbook accounts

Q16.

Aqua regia is a mixture of:

• A HNO₃ and HCl (1:3 ratio)
• B H₂SO₄ and HNO₃ during normal conditions
• C HCl and H₂SO₄ as generally observed
• D HNO₃ and H₃PO₄ in typical laboratory settings

Q17.

Which element is commonly used as a disinfectant and in PVC production?

• A Chlorine
• B Fluorine
• C Bromine
• D Iodine

Q18.

Which Group 15 element is the most abundant gas in the atmosphere?

• A phosphorus
• B arsenic
• C nitrogen
• D bismuth

Q19.

Ozone (O₃) is an allotrope of which Group 16 element?

• A oxygen
• B sulfur
• C selenium
• D tellurium

Q20.

The most electronegative element, found in Group 17, is:

• A chlorine
• B fluorine
• C bromine
• D iodine

Q21.

The inert pair effect in p-block heavy elements results in:

• A Lower oxidation states being more stable (e.g., Pb²⁺ more stable than Pb⁴⁺)
• B Higher oxidation states such as Pb⁴⁺ becoming the preferred state
• C All oxidation states being equally stable with no preference shown
• D A complete absence of any preferred oxidation state for these elements

Q22.

Which oxide of nitrogen is responsible for photochemical smog?

• A NO₂ (nitrogen dioxide)
• B N₂O (laughing gas)
• C NO (nitric oxide)
• D N₂O₅

Q23.

Preparation of HNO₃ by Ostwald process: the key oxidation step is:

• A 4NH₃ + 5O₂ → 4NO + 6H₂O (catalysed by Pt/Rh)
• B N₂ + O₂ → 2NO occurring directly without a catalyst at this stage
• C NO + O₂ → NO₂, the subsequent atmospheric oxidation step
• D 3NO₂ + H₂O → 2HNO₃ + NO, the final absorption step in water

Q24.

Why is nitrogen able to form multiple oxides (N₂O, NO, N₂O₃, NO₂, N₂O₄, N₂O₅)?

• A Nitrogen has multiple stable oxidation states (-3 to +5) because of variable bonding with oxygen
• B Nitrogen possesses accessible d orbitals that allow octet expansion in typical laboratory settings
• C Nitrogen is generally the most reactive element in the entire periodic table under usual circumstances
• D Nitrogen forms mainly ionic bonds with oxygen in each of these oxides according to most researchers

Q25.

Phosphine (PH₃) is a:

• A Toxic, foul-smelling gas used in semiconductor doping and as a fumigant
• B A sweet-smelling gas commonly used as a food flavouring agent
• C A chemically inert gas that does not react with common oxidisers
• D A dense liquid that condenses readily at room temperature

Q26.

The structure of PCl₅ in the gas phase is:

• A Trigonal bipyramidal (sp³d hybridisation)
• B Octahedral, using sp³d² hybridisation around phosphorus
• C Square planar, with phosphorus using dsp² hybridisation
• D Tetrahedral, using simple sp³ hybridisation around phosphorus

Q27.

In PCl₅, the axial P-Cl bonds are longer than equatorial P-Cl bonds because:

• A Axial bonds are perpendicular to 3 equatorial bond pairs (more repulsion, longer bond)
• B The chlorine atoms occupying axial positions are physically larger in the majority of cases studied
• C The phosphorus atom is somehow chemically different at each position as widely reported
• D The bond length difference arises mainly from the reaction temperature in standard practice

Q28.

H₃PO₃ is diprotic (not triprotic) because:

• A One P-H bond is not ionisable (P directly bonded to H does not donate H+)
• B The molecule actually contains mainly two hydrogen atoms in total under most conditions encountered
• C It is classified as a weak acid rather than a strong one as frequently observed in practice
• D It contains three separate -OH groups, most of which ionise in many documented cases

Q29.

The bleaching action of Cl₂ is due to:

• A Nascent oxygen released from Cl₂ + H₂O reaction oxidising the colour
• B The hydrochloric acid formed alongside the bleaching reaction
• C Cl₂ acting as a reducing agent that donates electrons to the dye
• D Cl₂ simply dissolving in water without any further chemical change

Q30.

Which of the following is an interhalogen compound?

• A ClF₃
• B Cl₂
• C NaCl
• D HCl

Q31.

The structure of XeF₄ is:

• A Square planar (2 lone pairs in octahedral arrangement)
• B Tetrahedral, with xenon using simple sp³ hybridisation
• C Trigonal pyramidal, with one lone pair occupying an apical site
• D Linear, with the two lone pairs positioned at right angles

Q32.

Sulfuric acid is a dehydrating agent because:

• A It has a strong affinity for water and removes H and OH as water from other compounds
• B It is generally classified as a strong acid that largely ionises according to conventional understanding
• C It functions mainly as an oxidising agent in this particular role in routine practice
• D It is largely miscible with water in all proportions overall in most cases under typical conditions

Q33.

The Contact process for H₂SO₄ uses which catalyst?

• A V₂O₅ (vanadium pentoxide)
• B Pt gauze, the catalyst used instead in the Ostwald process
• C Fe, the catalyst used instead in the Haber process
• D MnO₂, used instead as a catalyst in oxygen generation from KClO₃

Q34.

Which allotrope of sulfur is most stable at room temperature?

• A Rhombic sulfur (alpha-sulfur)
• B Monoclinic sulfur according to standard textbooks
• C Plastic sulfur in general practice
• D Amorphous sulfur as frequently described

Q35.

Ozone (O₃) acts as an oxidising agent because:

• A It decomposes to release nascent oxygen: O₃ → O₂ + [O]
• B It is thermodynamically more stable than ordinary O₂ gas
• C It readily forms stable compounds with the noble gases
• D It primarily functions as a reducing agent in most reactions

Q36.

Which reaction produces chlorine gas industrially (electrolytic process)?

• A Electrolysis of brine (NaCl solution) at the anode: 2Cl- → Cl₂ + 2e-
• B The thermal decomposition of solid sodium chloride at high temperature
• C The laboratory reaction of concentrated HCl with solid MnO₂
• D The direct combustion of sodium metal in chlorine gas

Q37.

What is the hybridisation of xenon in XeF₂?

• A sp³d (trigonal bipyramidal, linear molecule with 3 lone pairs)
• B sp³, giving a simple tetrahedral electron arrangement in most textbook accounts
• C sp², giving a trigonal planar electron arrangement during normal conditions
• D sp³d², giving an octahedral electron arrangement as generally observed

Q38.

Fuming sulfuric acid (oleum) is:

• A H₂SO₄ with dissolved SO₃ (pyrosulfuric acid, H₂S₂O₇)
• B Generally dilute aqueous H₂SO₄ at low concentration
• C H₂SO₄ existing largely as a gas under ordinary conditions
• D A direct mixture of concentrated H₂SO₄ with concentrated HNO₃

Q39.

Nitrogen pentoxide (N₂O₅) is the anhydride of:

• A HNO₃ (nitric acid)
• B HNO₂ (nitrous acid)
• C NO₂
• D NH₃

Q40.

Which element in Group 13 is amphoteric?

• A Aluminium (Al)
• B Boron (B)
• C Gallium (Ga)
• D Indium (In)

Q41.

Why does fluorine not exhibit positive oxidation states unlike other halogens?

• A F has the highest electronegativity and no d orbitals available for expansion of valence shell
• B Fluorine actually behaves chemically as a metal rather than as a non-metal in most textbook accounts
• C Fluorine is generally a far too large an atom to ever form higher oxidation states during normal conditions
• D Fluorine atoms are said to possess no lone pairs of electrons whatsoever as generally observed

Q42.

The photochemical smog formation involves which sequence?

• A NO₂ → NO + O; O + O₂ → O₃; O₃ + hydrocarbons → PAN and other irritants
• B Atmospheric CO₂ absorbing sunlight and directly forming smog particles
• C SO₂ reacting with ozone to form the bulk of urban photochemical smog
• D Ammonia reacting with atmospheric water vapour to form smog droplets

Q43.

Which nitrogen compound catalytically destroys stratospheric ozone?

• A NO and NO₂ (NOx from supersonic aircraft)
• B N₂O₅, a stable nitrogen oxide that does not catalyse ozone breakdown
• C HNO₃, the stable acid formed in the lower atmosphere from NOx
• D NH₃, a basic gas with no catalytic effect on stratospheric ozone

Q44.

In the hybridisation of SF₆, which orbital set does sulfur use?

• A sp³d² (one 3s, three 3p, two 3d orbitals)
• B sp³d, giving a trigonal bipyramidal geometry instead
• C sp³, giving a simple tetrahedral geometry instead
• D sp², giving a trigonal planar geometry instead

Q45.

Why does OF₂ have F-O-F angle (103.2°) less than H₂O (104.5°)?

• A F is more electronegative than H; bond pair electrons in O-F are pulled away from O more, reducing repulsion and decreasing angle
• B Fluorine is generally claimed to be a much more physically large atom than hydrogen overall as frequently observed in practice
• C The O-F bonds are claimed to be noticeably shorter in length than the O-H bonds found in water in many documented cases according to conventional understanding
• D The oxygen lone pairs are claimed to become physically larger in size once bonded to fluorine instead in routine practice overall

Q46.

The structure of H₃PO₄ has:

• A P in +5 state with 3 P-OH (ionisable) and one P=O (not ionisable), making it triprotic
• B Mainly a single ionisable hydrogen among the four present in most cases under typical conditions
• C A direct P-H bond that does not contribute any ionisable proton according to standard textbooks
• D All four hydrogen atoms largely ionisable, making it tetraprotic in general practice

Q47.

The reaction 2SO₂ + O₂ ⇌ 2SO₃ in the Contact process is exothermic. To maximise yield:

• A Low temperature and high pressure (Le Chatelier), but kinetics require compromise at ~450°C and ~1-2 atm
• B Operating at the highest practical reactor temperature regardless of the resulting yield as frequently described
• C Maintaining a very low pressure throughout the entire reactor vessel times in most textbook accounts
• D Combining a high reactor temperature with a low operating pressure to maximise yield during normal conditions

Q48.

Xenon forms compounds with fluorine and oxygen because:

• A Xe has large atomic radius and low ionisation energy, making it accessible to attack by highly electronegative F
• B Xenon possesses readily accessible low-energy d orbitals it can use for bonding as generally observed in typical laboratory settings
• C Xenon actually behaves chemically as a metal under ordinary laboratory conditions under usual circumstances
• D Xenon reacts readily with the vast majority of elements on the periodic table according to most researchers

Q49.

In the reaction between Cl₂ and hot concentrated NaOH, the product is:

• A NaClO₃ (sodium chlorate) and NaCl
• B NaOCl and NaCl (cold dilute NaOH gives hypochlorite)
• C NaCl only
• D NaClO₄

Q50.

The bond angle in SO₂ is 119° (close to 120°). This suggests:

• A sp² hybridisation of S with one lone pair in one sp² orbital; the lone pair causes slight compression from ideal 120°
• B sp³ hybridisation of sulfur with two separate lone pairs occupying tetrahedral sites in the majority of cases studied
• C sp hybridisation of sulfur producing a perfectly linear electron-pair arrangement as widely reported in standard practice
• D A perfectly linear molecular geometry showing an exact 180 degree bond angle under most conditions encountered as frequently observed in practice

Q51.

Which p-block element exhibits the widest range of allotropes?

• A Carbon (diamond, graphite, graphene, fullerene, amorphous carbon, nanotubes...)
• B Sulfur, which forms mainly the rhombic and monoclinic crystal forms in many documented cases
• C Phosphorus, which forms mainly the white and red allotropic forms according to conventional understanding
• D Oxygen, which forms mainly the dioxygen and ozone allotropic forms in routine practice

Q52.

In concentrated H₂SO₄, the acid acts as a sulfonating agent because:

• A The electrophilic SO₃ (from equilibrium H₂S₂O₇ ⇌ SO₃ + H₂SO₄) attacks the aromatic ring
• B H₂SO₄ generally ionises largely into H+ and sulfate ions in solution overall in most cases
• C H₂SO₄ acts here mainly as a reducing agent toward the aromatic ring under typical conditions
• D A free H+ ion directly attacks the aromatic ring as the electrophile according to standard textbooks

Q53.

Why do noble gases have very high first ionisation energies?

• A Completely filled valence shells + high effective nuclear charge in their period
• B They are generally defined as chemically inert by convention in general practice
• C They possess no electrons available for removal as frequently described in most textbook accounts
• D They exist mainly as gases under standard conditions during normal conditions

Q54.

The dihedral angle in H₂O₂ (approx 111°) compared to H₂O₂ in crystal form (approx 90°) shows that:

• A Lone pair repulsion and crystal packing forces influence the conformation differently
• B H₂O₂ acquires an aromatic delocalised structure once crystallised as generally observed
• C The crystalline form has an largely different chemical formula in typical laboratory settings
• D The O-O and O-H bond lengths change substantially upon crystallisation under usual circumstances

Q55.

The acid strength order of oxyacids of chlorine is:

• A HClO < HClO2 < HClO3 < HClO4
• B HClO4 < HClO3 < HClO2 < HClO
• C HClO = HClO4
• D All equal

Q56.

Why is PCl₅ hydrolysed in water but not SF₆?

• A PCl₅ has an accessible P centre; SF₆'s S is sterically shielded by 6 F atoms preventing water attack
• B SF₆ is actually an ionic compound that strongly resists hydrolysis in water according to most researchers
• C PCl₅ is supposedly thermodynamically more stable than SF₆ toward hydrolysis in the majority of cases studied
• D The difference arises mainly from the temperature of the water sample used as widely reported in standard practice

Q57.

The correct order of acidic strength of the hydrogen halides is:

• A HF > HCl > HBr > HI
• B HI > HBr > HCl > HF
• C HCl > HF > HBr > HI
• D HBr > HI > HCl > HF

Q58.

In the Ostwald process for nitric acid, ammonia is first oxidised over a catalyst of:

• A iron granules
• B platinum–rhodium gauze
• C vanadium pentoxide
• D finely divided nickel

Q59.

In the interhalogen compound ClF₃, the hybridisation of the central chlorine atom is:

• A sp³
• B sp³d
• C sp³d²
• D sp²

Q60.

The first noble-gas compound to be prepared, XePtF₆, was formed from which noble gas?

• A helium
• B neon
• C argon
• D xenon