UEE Chemistry (ЭЕШ Хими) (Mongolia)

Which of the following sets of quantum numbers (n, l, ml, ms) represents an allowed state for an electron in an atom?

• An = 4, l = 0, ml = 0, ms = +1
• Bn = 2, l = 2, ml = 0, ms = -1/2
• Cn = 3, l = 1, ml = +2, ms = +1/2
• Dn = 3, l = 2, ml = -1, ms = +1/2

What is the ground-state electron configuration of a neutral copper atom (29Cu)?

• A[Ar] 3d¹⁰ 4s¹
• B[Ar] 3d⁹ 4s²
• C[Ar] 3d⁸ 4s² 4p¹
• D[Ar] 3d¹⁰ 4p¹

Moving from left to right across Period 3 of the Periodic Table (from Na to Cl), how do atomic radius and first ionization energy typically change?

• ABoth atomic radius and first ionization energy decrease
• BAtomic radius increases while first ionization energy decreases
• CBoth atomic radius and first ionization energy increase
• DAtomic radius decreases while first ionization energy generally increases

Why does nitrogen (Z = 7) have a higher first ionization energy (1402 kJ/mol) than oxygen (Z = 8, 1314 kJ/mol), despite oxygen having a greater nuclear charge?

• ANitrogen has a stable half-filled 2p³ subshell, whereas oxygen has paired electrons in a…
• BOxygen has a larger atomic radius than nitrogen, making its outer electrons easier to rem…
• CNitrogen's 2p electrons provide greater core shielding than oxygen's 2p electrons
• DOxygen's valence electrons occupy a higher principal energy level than nitrogen's valence…

An ion contains 35 protons, 45 neutrons, and 36 electrons. What is the correct isotopic representation for this species?

• A⁸⁰₃₅Br⁻
• B⁸⁰₃₅Br⁺
• C⁷⁰₃₅Br⁻
• D⁸⁰₄₅Rh⁻

What is the ground-state electron configuration of the iron(III) cation, Fe³⁺ (atomic number Z = 26)?

• A[Ar] 3d⁵
• B[Ar] 3d³ 4s²
• C[Ar] 3d⁶
• D[Ar] 3d⁴ 4s¹

Which of the following elements has the highest electronegativity value on the Pauling scale?

• ANitrogen (N)
• BChlorine (Cl)
• COxygen (O)
• DFluorine (F)

Which of the following isoelectronic ions has the largest ionic radius: N³⁻, O²⁻, F⁻, or Na⁺?

• AN³⁻
• BNa⁺
• CF⁻
• DO²⁻

Calculate the wavelength of the photon emitted during an electronic transition from n = 4 to n = 2 in a hydrogen atom (Rydberg constant R_H = 1.097 × 10⁷ m⁻¹).

• A486 nm
• B656 nm
• C434 nm
• D410 nm

How many unpaired electrons are present in the ground state of an isolated phosphorus atom (Z = 15)?

• A3
• B1
• C2
• D5

Which of the following compounds contains both ionic and covalent chemical bonds?

• ACarbon tetrachloride (CCl₄)
• BMethane (CH₄)
• CSodium chloride (NaCl)
• DAmmonium chloride (NH₄Cl)

According to VSEPR theory, what are the electron-domain geometry and molecular shape of sulfur tetrafluoride (SF₄)?

• ATrigonal bipyramidal electron-domain geometry and seesaw molecular shape
• BOctahedral electron-domain geometry and square planar molecular shape
• CTetrahedral electron-domain geometry and tetrahedral molecular shape
• DTrigonal bipyramidal electron-domain geometry and T-shaped molecular shape

What is the hybridization of the central phosphorus atom in gaseous phosphorus pentachloride (PCl₅)?

• Asp³d
• Bsp³
• Csp³d²
• Dsp²

Why is the normal boiling point of water (H₂O, 100 °C) substantially higher than that of hydrogen sulfide (H₂S, -60 °C), despite H₂S having a greater molecular mass?

• AWater molecules form extensive intermolecular hydrogen bonds, whereas H₂S molecules inter…
• BThe covalent H–O bond is weaker than the H–S bond, allowing liquid water to pack more den…
• CH₂S is completely non-polar and experiences only London dispersion forces
• DWater has a higher molecular weight than hydrogen sulfide

How many sigma (σ) and pi (π) bonds are present in a molecule of ethyne (acetylene, H–C≡C–H)?

• A3 sigma (σ) bonds and 2 pi (π) bonds
• B2 sigma (σ) bonds and 3 pi (π) bonds
• C5 sigma (σ) bonds and 0 pi (π) bonds
• D1 sigma (σ) bond and 2 pi (π) bonds

Which of the following molecules has a net dipole moment (is polar)?

• ASulfur tetrafluoride (SF₄)
• BCarbon tetrachloride (CCl₄)
• CBoron trifluoride (BF₃)
• DXenon tetrafluoride (XeF₄)

According to Molecular Orbital (MO) theory, what is the bond order and magnetic behavior of the neutral diatomic oxygen molecule (O₂)?

• ABond order = 2, paramagnetic with two unpaired electrons
• BBond order = 2, diamagnetic with all electrons paired
• CBond order = 2.5, paramagnetic with one unpaired electron
• DBond order = 1.5, paramagnetic with one unpaired electron

Predict the molecular geometry and ideal bond angle of the triiodide anion (I₃⁻) using VSEPR theory.

• ALinear with a bond angle of 180°
• BBent with a bond angle of ~104.5°
• CTrigonal planar with a bond angle of 120°
• DT-shaped with bond angles of 90° and 180°

Which of the following substances forms a covalent network (macromolecular) crystal lattice in its solid state?

• ASucrose (C₁₂H₂₂O₁₁)
• BCarbon dioxide (CO₂)
• CSodium chloride (NaCl)
• DSilicon dioxide (SiO₂)

Based on electronegativity differences, which of the following diatomic bonds has the greatest ionic character (highest bond polarity)?

• AH–F
• BH–Cl
• CH–Br
• DH–I

Use Hess's Law to calculate the standard enthalpy of formation (ΔHf°) of methane from its elements: C(graphite) + 2H₂(g) → CH₄(g), given the following thermochemical equations: (1) C(graphite) + O₂(g) → CO₂(g), ΔH₁ = -393.5 kJ/mol (2) H₂(g) + 1/2 O₂(g) → H₂O(l), ΔH₂ = -285.8 kJ/mol (3) CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l), ΔH₃ = -890.3 kJ/mol

• A+74.8 kJ/mol
• B-74.8 kJ/mol
• C-211.0 kJ/mol
• D-1569.6 kJ/mol

For a chemical reaction with standard enthalpy change ΔH° = +40.0 kJ/mol and standard entropy change ΔS° = +100 J/(mol·K), at which temperatures will the reaction be thermodynamically spontaneous under standard conditions?

• AAt all temperatures below 250 K
• BAt all temperatures below 400 K
• CThe reaction is non-spontaneous at all temperatures
• DAt all temperatures above 400 K (127 °C)

For the reaction 2A + B → C, initial rate data were obtained at 25 °C: Experiment 1: [A] = 0.10 M, [B] = 0.10 M, Initial Rate = 2.0 × 10⁻³ M/s Experiment 2: [A] = 0.20 M, [B] = 0.10 M, Initial Rate = 8.0 × 10⁻³ M/s Experiment 3: [A] = 0.10 M, [B] = 0.20 M, Initial Rate = 4.0 × 10⁻³ M/s What is the differential rate law and overall reaction order?

• ARate = k[A][B], overall order 2
• BRate = k[A]²[B]², overall order 4
• CRate = k[A][B]², overall order 3
• DRate = k[A]²[B], overall order 3

According to collision theory and the Arrhenius equation (k = A·e^(-Ea/RT)), what is the primary mechanism by which a positive catalyst accelerates a chemical reaction?

• AIt increases the average kinetic energy and temperature of the reacting particles
• BIt shifts the position of chemical equilibrium toward higher product concentration
• CIt increases the reaction enthalpy (ΔH), making the overall reaction more exothermic
• DIt provides an alternative reaction pathway with a lower activation energy (Ea), increasi…

Consider the Haber-Bosch synthesis of ammonia: N₂(g) + 3H₂(g) ⇌ 2NH₃(g), ΔH° = -92.2 kJ/mol. According to Le Chatelier's principle, which combination of temperature and pressure shifts the equilibrium to produce the highest equilibrium yield of NH₃?

• AHigh temperature and low pressure
• BHigh temperature and high pressure
• CLow temperature and high pressure
• DLow temperature and low pressure

What is the correct equilibrium constant expression (Kc) for the thermal decomposition of limestone: CaCO₃(s) ⇌ CaO(s) + CO₂(g)?

• AKc = [CaO] / [CaCO₃]
• BKc = [CaO][CO₂] / [CaCO₃]
• CKc = [CO₂] / [CaCO₃]
• DKc = [CO₂]

For the gas-phase contact oxidation reaction 2SO₂(g) + O₂(g) ⇌ 2SO₃(g) at temperature T, what is the exact mathematical relationship between Kp and Kc?

• AKp = Kc · (RT)
• BKp = Kc · (RT)²
• CKp = Kc
• DKp = Kc / (RT)

In which of the following physical or chemical processes does the standard entropy of the system increase (ΔS° > 0)?

• A2H₂(g) + O₂(g) → 2H₂O(l)
• BNH₄Cl(s) → NH₃(g) + HCl(g)
• CN₂(g) + 3H₂(g) → 2NH₃(g)
• DH₂O(g) → H₂O(l)

A first-order decomposition reaction has a rate constant k = 0.0231 min⁻¹. What is its half-life (t₁/₂), and how long will it take for the reactant concentration to decrease to 12.5% of its initial value?

• At₁/₂ = 15 min; 45 min for 12.5%
• Bt₁/₂ = 20 min; 60 min for 12.5%
• Ct₁/₂ = 60 min; 180 min for 12.5%
• Dt₁/₂ = 30 min; 90 min for 12.5%

By international IUPAC definition, which of the following chemical species has a standard molar enthalpy of formation (ΔHf°) strictly equal to 0 kJ/mol at 298 K and 100 kPa (1 bar)?

• AO₂(g)
• BO₃(g)
• CC(diamond)
• DBr₂(g)

When metallic sodium is heated and burned in an excess of pure oxygen gas, what is the principal chemical product formed?

• ASodium oxide (Na₂O)
• BSodium peroxide (Na₂O₂)
• CSodium superoxide (NaO₂)
• DSodium hydroxide (NaOH)

How do the water solubilities of Group 2 alkaline earth metal sulfates (from MgSO₄ to BaSO₄) and hydroxides (from Mg(OH)₂ to Ba(OH)₂) change down the group from top to bottom?

• ABoth sulfate solubility and hydroxide solubility increase down the group
• BSulfate solubility increases, while hydroxide solubility decreases down the group
• CSulfate solubility decreases, while hydroxide solubility increases down the group
• DBoth sulfate solubility and hydroxide solubility decrease down the group

Based on the standard reduction potentials and oxidizing abilities of the elemental halogens, which of the following single-displacement reactions will occur spontaneously in aqueous solution?

• ACl₂(aq) + 2NaBr(aq) → 2NaCl(aq) + Br₂(aq)
• BI₂(aq) + 2NaCl(aq) → 2NaI(aq) + Cl₂(aq)
• CBr₂(aq) + 2NaF(aq) → 2NaBr(aq) + F₂(aq)
• DI₂(aq) + 2NaBr(aq) → 2NaI(aq) + Br₂(aq)

In the industrial Contact process for manufacturing sulfuric acid (H₂SO₄), why is sulfur trioxide (SO₃) gas absorbed into 98% concentrated sulfuric acid to form oleum (H₂S₂O₇) rather than being bubbled directly into liquid water?

• ASulfur trioxide does not react chemically with pure liquid water
• BThe direct reaction with liquid water is endothermic and ceases without continuous extern…
• CWater chemically decomposes sulfur trioxide into sulfur dioxide and oxygen gas
• DThe direct reaction with water is violently exothermic and vaporizes water into a dense,…

In the first industrial stage of the Ostwald process for nitric acid manufacture, ammonia is catalytically oxidized to nitric oxide: 4NH₃(g) + 5O₂(g) → 4NO(g) + 6H₂O(g). What catalyst and temperature are used?

• AIron catalyst with Al₂O₃ promoter at 450 °C
• BPlatinum-rhodium (Pt-Rh) gauze catalyst at ~800–900 °C
• CVanadium pentoxide (V₂O₅) at 450 °C
• DFinely divided nickel catalyst at 150 °C

Which statement correctly explains the difference in chemical reactivity and structure between white phosphorus and red phosphorus?

• AWhite phosphorus forms a polymeric chain and is stable in air, whereas red phosphorus is…
• BRed phosphorus consists of discrete P₄ molecules, whereas white phosphorus is a giant net…
• CWhite phosphorus consists of discrete tetrahedral P₄ molecules with 60° bond angles causi…
• DBoth white and red phosphorus are equally flammable and dissolve readily in polar solvent…

Why is carbon dioxide (CO₂) a gas at standard temperature and pressure, whereas silicon dioxide (SiO₂) is a high-melting crystalline solid, despite both C and Si belonging to Group 14?

• ACarbon's small 2p orbitals form strong pπ-pπ double bonds with oxygen producing discrete…
• BSilicon has a much lower atomic mass than carbon, causing it to condense more readily
• CCO₂ is an ionic crystal that sublimes easily, whereas SiO₂ forms coordinate covalent bonds
• DSilicon forms a linear diatomic molecule that polymerizes only upon cooling to absolute z…

Which noble gas was the first to have a true chemical compound synthesized (by Neil Bartlett in 1962), and what key property enabled this reaction?

• AHelium, due to its high ionization energy
• BArgon, due to its low polarizability
• CNeon, due to its high nuclear charge
• DXenon, because its first ionization energy (1170 kJ/mol) is comparable to that of molecul…

Which of the following pairs contains only amphoteric oxides that can react with both strong acids and strong aqueous bases?

• ANa₂O and CaO
• BCO and NO
• CSO₂ and CO₂
• DAl₂O₃ and ZnO

What unique type of chemical bonding accounts for the electron-deficient structure of diborane (B₂H₆)?

• AA standard two-center two-electron (2c-2e) B–B single covalent bond
• BDelocalized aromatic π-bonding between boron atoms
• CThree-center two-electron (3c-2e) bridging B–H–B bonds ("banana" bonds)
• DPure ionic bonding between B³⁺ cations and H⁻ hydride anions

What are the oxidation state and coordination number of cobalt in the coordination compound [Co(NH₃)₅Cl]Cl₂?

• AOxidation state +2; coordination number 5
• BOxidation state +3; coordination number 6
• COxidation state +3; coordination number 5
• DOxidation state +1; coordination number 6

Why do aqueous transition metal complex ions, such as [Cu(H₂O)₆]²⁺ and [Fe(H₂O)₆]³⁺, typically exhibit characteristic bright colors?

• ANuclear excitation and radioactive emission of gamma photons
• BIntramolecular vibrations of hydrogen bonds in the surrounding hydration sphere
• Cd-d electronic transitions where electrons absorb specific wavelengths of visible light t…
• DComplete ionization and ejection of outer valence s-electrons into the solvent

When dilute aqueous sodium hydroxide (NaOH) is added dropwise to a solution containing iron(II) ions (Fe²⁺), a precipitate forms that subsequently changes color upon exposure to atmospheric air. What are the identity and color transitions of this precipitate?

• AA white gelatinous precipitate forms that dissolves upon bubbling air through the solution
• BA deep-blue precipitate forms that immediately dissolves in excess alkali to form a color…
• CA dark-brown precipitate forms immediately that turns bright yellow upon exposure to air
• DA dirty-green precipitate of Fe(OH)₂ forms, which gradually oxidizes in air to form reddi…

Which analytical reagent is used to confirm the presence of sulfate ions (SO₄²⁻) in an aqueous sample, and what is the characteristic positive observation?

• ASilver nitrate (AgNO₃) in concentrated ammonia, forming a yellow precipitate
• BBarium chloride (BaCl₂) acidified with dilute hydrochloric acid (HCl), forming a white pr…
• CSodium hydroxide (NaOH) with heating, evolving a pungent alkaline gas
• DPotassium permanganate (KMnO₄) acidified with sulfuric acid, which is decolorized

An unknown white solid salt is analyzed: (1) Its aqueous solution yields a white precipitate with AgNO₃ that dissolves completely in dilute aqueous ammonia. (2) Adding BaCl₂ produces no precipitate. (3) A flame test yields a lilac (violet) flame through cobalt blue glass. What is the formula of the salt?

• ANaCl
• BBaCl₂
• CKCl
• DK₂SO₄

According to the Brønsted-Lowry acid-base theory, what is the conjugate base of the dihydrogen phosphate ion (H₂PO₄⁻)?

• AH₃PO₄
• BP₂O₇⁴⁻
• CPO₄³⁻
• DHPO₄²⁻

Which of the following salts dissolves in pure water at 25 °C to produce an acidic solution (pH < 7)?

• ASodium acetate (CH₃COONa)
• BPotassium nitrate (KNO₃)
• CSodium carbonate (Na₂CO₃)
• DAmmonium chloride (NH₄Cl)

What is the magnetic behavior and number of unpaired electrons in the low-spin octahedral complex ion [Fe(CN)₆]⁴⁻?

• AParamagnetic with 4 unpaired electrons
• BParamagnetic with 2 unpaired electrons
• CDiamagnetic with 0 unpaired electrons
• DDiamagnetic with 1 unpaired electron