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NY Regents Chemistry study materials
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NY Regents Chemistry practice questions

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Question 1Matter, Energy, and Measurement

A sample of a pure substance has a fixed mass and a fixed volume, and its particles are locked in an ordered pattern that only vibrate in place. Which classification best fits this sample?

  1. A gas
  2. A crystalline solid Correct answer.
  3. A liquid
  4. A homogeneous mixture

Explanation

A crystalline solid has particles arranged in a repeating, ordered lattice and can only vibrate about fixed positions, so both shape and volume are definite. A homogeneous mixture has variable composition, while liquids and gases lack a fixed ordered lattice.

Question 2Matter, Energy, and Measurement

Which statement describes a chemical property of a sample of iron rather than a physical property?

  1. Iron has a density of about 7.9 g/cm³ at room temperature.
  2. Iron melts at 1538 °C under standard pressure.
  3. Iron reacts with oxygen in moist air to form rust. Correct answer.
  4. Iron conducts electricity in the solid state.

Explanation

A chemical property describes how a substance changes into a different substance, such as iron combining with oxygen to form iron oxide. Density, melting point, and conductivity are measured without changing the identity of the iron.

Question 3Matter, Energy, and Measurement

A student heats a liquid in an open beaker and observes bubbles forming and escaping while the temperature stays constant at 100 °C. Which change is occurring?

  1. A physical change, because the liquid is freezing
  2. A chemical change, because the temperature is constant
  3. A chemical change, because bubbles of a new gas appear
  4. A physical change, because the liquid is vaporizing Correct answer.

Explanation

Boiling is a phase change in which liquid particles gain enough energy to escape as vapor; the substance's identity is unchanged, so it is physical. Constant temperature during boiling is expected for a pure substance at its boiling point and does not indicate a chemical reaction.

Question 4Matter, Energy, and Measurement

Which term best describes a mixture in which the different components are visibly distinct and can be separated by hand or filtration?

  1. An element
  2. A compound
  3. A solution
  4. A heterogeneous mixture Correct answer.

Explanation

A heterogeneous mixture has components that are not uniformly distributed, so different regions have different composition and can often be separated physically. Compounds and elements are pure substances, and a solution is uniform throughout.

Question 5Matter, Energy, and Measurement

A liquid is poured into a graduated cylinder and the bottom of the meniscus reads 24.6 mL. The liquid is then transferred completely into a beaker and weighed. Which measurement is a derived quantity rather than a direct reading from an instrument?

  1. The volume of 24.6 mL
  2. The temperature of the liquid in °C
  3. The mass of the liquid in grams
  4. The density of the liquid in g/mL Correct answer.

Explanation

Density is calculated by dividing measured mass by measured volume, so it is derived from two direct measurements. Volume, mass, and temperature are each read directly from a measuring device.

Question 6Matter, Energy, and Measurement

A metal block is placed on a balance that reads 54.0 g, and its volume is found to be 20.0 cm³ by displacement. What is the density of the metal?

  1. 0.370 g/cm³
  2. 2.70 g/cm³ Correct answer.
  3. 74.0 g/cm³
  4. 20.0 g/cm³

Explanation

Density equals mass divided by volume, so 54.0 g ÷ 20.0 cm³ = 2.70 g/cm³. The result carries three significant figures because both measurements have three.

Question 7Matter, Energy, and Measurement

Which observation is the best evidence that a new substance has formed during a reaction?

  1. The mixture is stirred more rapidly
  2. The total mass of the system stays constant
  3. The container becomes warm to the touch
  4. A solid appears when two clear solutions are mixed Correct answer.

Explanation

A solid forming from two clear solutions is a precipitate, which indicates that dissolved ions combined into an insoluble new compound. Warming and constant mass can accompany physical changes as well, and stirring does not indicate a reaction.

Question 8Matter, Energy, and Measurement

In the SI system, which unit is used to express the amount of a substance in terms of the number of representative particles?

  1. The kelvin
  2. The gram
  3. The joule
  4. The mole Correct answer.

Explanation

The mole is the SI base unit for amount of substance and contains Avogadro's number of representative particles. The gram measures mass, the kelvin measures temperature, and the joule measures energy.

Question 9Matter, Energy, and Measurement

A student records the mass of a sample three times as 12.51 g, 12.49 g, and 12.50 g. The accepted value is 13.20 g. Which statement about the data is accurate?

  1. The data are both accurate and precise
  2. The data are precise but not accurate Correct answer.
  3. The data are neither precise nor accurate
  4. The data are accurate but not precise

Explanation

Precision describes how closely repeated measurements agree, and these three trials differ by only 0.02 g, so they are precise. Accuracy describes closeness to the accepted value, and all three trials are about 0.7 g below 13.20 g, so they are inaccurate.

Question 10Matter, Energy, and Measurement

How many significant figures are in the measurement 0.004060 g?

  1. Five
  2. Six
  3. Four Correct answer.
  4. Three

Explanation

Leading zeros are never significant, so the zeros before the 4 do not count. The digits 4, 0, 6, and the trailing 0 after the 6 are all significant, giving four significant figures.

Question 11Matter, Energy, and Measurement

A sample of ethanol has a mass of 39.45 g and a volume of 50.0 mL. When expressed to the correct number of significant figures, what is its density?

  1. 0.7890 g/mL
  2. 0.789 g/mL Correct answer.
  3. 0.8 g/mL
  4. 0.79 g/mL

Explanation

Dividing 39.45 g by 50.0 mL gives 0.789 g/mL. Because the volume measurement has three significant figures, the quotient is limited to three, so 0.789 g/mL is correct.

Question 12Matter, Energy, and Measurement

A 25.0 g sample of an unknown metal absorbs 214 J of heat and its temperature rises from 20.0 °C to 30.0 °C. Using q = mCΔT, what is the specific heat capacity of the metal?

  1. 8.56 J/(g·°C)
  2. 85.6 J/(g·°C)
  3. 1.17 J/(g·°C)
  4. 0.856 J/(g·°C) Correct answer.

Explanation

Rearranging q = mCΔT gives C = q ÷ (mΔT) = 214 J ÷ (25.0 g × 10.0 °C) = 0.856 J/(g·°C). The temperature change is 10.0 °C, and the units follow from joules per gram per degree.

Question 13Matter, Energy, and Measurement

A 100.0 g sample of water at 25.0 °C gains 4180 J of heat. The specific heat of water is 4.18 J/(g·°C). What is the final temperature of the water?

  1. 15.0 °C
  2. 35.0 °C Correct answer.
  3. 10.0 °C
  4. 30.0 °C

Explanation

The temperature change is ΔT = q ÷ (mC) = 4180 J ÷ (100.0 g × 4.18 J/(g·°C)) = 10.0 °C. Adding this change to the initial 25.0 °C gives a final temperature of 35.0 °C.

Question 14Matter, Energy, and Measurement

A reaction releases 350 J of energy to the surroundings as it proceeds in an insulated container. Which description of the reaction is correct?

  1. It is exothermic, and the surroundings warm Correct answer.
  2. It is endothermic, and the surroundings warm
  3. It is exothermic, and the surroundings cool
  4. It is endothermic, and the surroundings cool

Explanation

An exothermic reaction transfers energy from the system to the surroundings, so the surroundings gain thermal energy and warm. Endothermic reactions absorb energy and cool the surroundings.

Question 15Matter, Energy, and Measurement

In a potential energy diagram, the products are drawn at a higher energy level than the reactants and the activation energy is labeled. Which statement about this reaction is correct?

  1. The reaction is exothermic, and the activation energy equals the total energy released
  2. The reaction is endothermic, and the activation energy is measured from the products to the peak
  3. The reaction is exothermic, and the activation energy is the difference between reactant and product energy
  4. The reaction is endothermic, and the activation energy is measured from the reactants to the peak Correct answer.

Explanation

When products lie above reactants, the system has absorbed net energy, so the reaction is endothermic. Activation energy is always the energy needed to reach the transition-state peak, measured from the reactants' energy level.

Question 16Matter, Energy, and Measurement

Which change in conditions will increase the rate at which a solid dissolves in water?

  1. Cooling the water
  2. Using larger pieces of the solid
  3. Stirring the mixture Correct answer.
  4. Increasing the pressure above the water

Explanation

Stirring continually brings fresh solvent into contact with the solid surface and carries dissolved particles away, increasing the dissolution rate. Cooling, larger pieces, and pressure changes on a liquid do not speed dissolution.

Question 17Matter, Energy, and Measurement

A sample of gas is held at constant temperature while its volume is reduced from 4.0 L to 1.0 L. According to Boyle's law, what happens to the pressure?

  1. It stays the same because temperature is constant
  2. It doubles
  3. It is reduced to one-fourth of its original value
  4. It becomes four times its original value Correct answer.

Explanation

Boyle's law states that at constant temperature, pressure and volume are inversely proportional, so P₁V₁ = P₂V₂. Reducing volume by a factor of four raises pressure by a factor of four.

Question 18Matter, Energy, and Measurement

A gas occupies 2.00 L at 300 K. At constant pressure, what volume does it occupy at 600 K?

  1. 2.00 L
  2. 8.00 L
  3. 4.00 L Correct answer.
  4. 1.00 L

Explanation

Charles's law states that volume and absolute temperature are directly proportional at constant pressure, so V₂ = V₁(T₂/T₁) = 2.00 L × (600 K/300 K) = 4.00 L. Doubling the kelvin temperature doubles the volume.

Question 19Matter, Energy, and Measurement

A sealed rigid container holds a gas at 27 °C and 100 kPa. If the gas is heated to 327 °C, what is the new pressure?

  1. 50 kPa
  2. 150 kPa
  3. 200 kPa Correct answer.
  4. 100 kPa

Explanation

Gay-Lussac's law relates pressure and absolute temperature at constant volume: P₂ = P₁(T₂/T₁). Converting to kelvin gives 300 K and 600 K, so P₂ = 100 kPa × (600/300) = 200 kPa.

Question 20Matter, Energy, and Measurement

A 36.0 g sample of carbon contains how many moles of carbon atoms? The molar mass of carbon is 12.0 g/mol.

  1. 12.0 mol
  2. 3.00 mol Correct answer.
  3. 0.333 mol
  4. 432 mol

Explanation

Moles equal mass divided by molar mass: 36.0 g ÷ 12.0 g/mol = 3.00 mol. Multiplying instead of dividing or using the molar mass directly gives incorrect values.

Question 21Matter, Energy, and Measurement

How many atoms are present in 0.500 mol of helium gas? Avogadro's number is 6.02 × 10²³.

  1. 1.20 × 10²⁴ atoms
  2. 1.20 × 10²³ atoms
  3. 6.02 × 10²³ atoms
  4. 3.01 × 10²³ atoms Correct answer.

Explanation

Multiplying the number of moles by Avogadro's number gives 0.500 × 6.02 × 10²³ = 3.01 × 10²³ atoms. Helium is monatomic, so each particle is one atom.

Question 22Matter, Energy, and Measurement

A closed system undergoes a chemical reaction in which a gas is produced and escapes through a small vent. Which statement about the mass of the remaining contents is correct?

  1. The mass cannot be predicted from the information given
  2. The mass decreases because matter leaves the system Correct answer.
  3. The mass increases because a gas was produced
  4. The mass stays the same because mass is always conserved

Explanation

The law of conservation of mass applies to a closed system with no exchange of matter. Because the vent lets gaseous product escape, matter leaves the open system and the remaining mass decreases.

Question 23Matter, Energy, and Measurement

A student wants to separate a mixture of sand and dissolved salt water. Which sequence of techniques will accomplish this?

  1. Evaporation followed by filtration
  2. Chromatography followed by distillation
  3. Distillation followed by filtration
  4. Filtration followed by evaporation Correct answer.

Explanation

Filtration first removes the insoluble sand from the saltwater. Evaporating the filtrate then leaves the dissolved salt as a solid residue.

Question 24Matter, Energy, and Measurement

A mixture of two liquids with different boiling points is separated by fractional distillation. Which principle explains why the liquid with the lower boiling point is collected first?

  1. It reacts chemically with the column packing before the other liquid
  2. It has the greater density and settles at the bottom
  3. It has the higher vapor pressure at a given temperature and vaporizes more readily Correct answer.
  4. It has stronger intermolecular forces and escapes the liquid phase more easily

Explanation

A liquid with a lower boiling point has weaker intermolecular forces and a higher vapor pressure at any given temperature, so it vaporizes more readily and travels up the column first. Density and chemical reaction with the packing are not the basis of fractional distillation.

Question 25Matter, Energy, and Measurement

A sample of an element is found to be composed of atoms with different mass numbers but identical chemical behavior. Which term describes these atoms?

  1. Allotropes
  2. Isomers
  3. Ions
  4. Isotopes Correct answer.

Explanation

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons, giving different mass numbers while chemical behavior stays nearly identical. Ions, allotropes, and isomers describe different structural situations.

Question 26Matter, Energy, and Measurement

A student heats a 12.0 g sample of an unknown liquid in a calorimeter and finds that it absorbs 1.50 kJ while its temperature rises by 25.0 °C. What is the specific heat capacity of the liquid, expressed in J/(g·°C)?

  1. 0.00500 J/(g·°C)
  2. 0.200 J/(g·°C)
  3. 50.0 J/(g·°C)
  4. 5.00 J/(g·°C) Correct answer.

Explanation

Rearranging q = m·c·ΔT gives c = q/(m·ΔT). Converting 1.50 kJ to 1500 J and substituting gives c = 1500 J ÷ (12.0 g × 25.0 °C) = 5.00 J/(g·°C). The result is reasonable because it lies between the specific heats of common metals and water.

Question 27Matter, Energy, and Measurement

A sample of matter has a definite volume but takes the shape of its container, and its particles are close together yet able to slide past one another. In which state of matter is the sample?

  1. Liquid Correct answer.
  2. Gas
  3. Solid
  4. Plasma

Explanation

A liquid has a definite volume but no definite shape because its particles remain close together while moving past one another. Solids keep both a definite shape and volume, while gases fill their containers because their particles are far apart. The description therefore matches the liquid state.

Question 28Matter, Energy, and Measurement

A sealed flask contains a mixture of nitrogen and oxygen gas. Which statement correctly describes the particles in this mixture?

  1. The nitrogen and oxygen particles are chemically bonded to each other.
  2. The mixture has a fixed composition that cannot vary.
  3. The particles of each gas are uniformly distributed and can be separated by physical means. Correct answer.
  4. The two gases react to form a single new compound.

Explanation

A mixture contains two or more substances that are physically combined, so its components keep their own identities and can be separated by physical methods. In a gas mixture the particles are spread uniformly throughout the container. A compound, by contrast, has components chemically bonded in a fixed ratio.

Question 29Matter, Energy, and Measurement

A chemistry student reads a thermometer that is marked in whole degrees and records the boiling point of a liquid as 78 °C. Which statement best describes this measurement?

  1. It has two significant figures and an uncertainty of about ±1 °C. Correct answer.
  2. It has zero significant figures because no decimal is shown.
  3. It has one significant figure because the reading is a whole number.
  4. It has an infinite number of significant figures.

Explanation

When an instrument is marked in whole units, the recorded value is estimated to the nearest mark, giving an uncertainty of about half the smallest division, roughly ±1 °C here. The digits 7 and 8 are both significant, so the measurement has two significant figures.

Question 30Matter, Energy, and Measurement

A 250.0 mL sample of a salt solution has a mass of 262.5 g. What is the density of the solution?

  1. 13.1 g/mL
  2. 1050 g/mL
  3. 1.050 g/mL Correct answer.
  4. 0.9524 g/mL

Explanation

Density is mass divided by volume, so d = 262.5 g ÷ 250.0 mL = 1.050 g/mL. Both measurements have four significant figures, so the answer is reported to four significant figures.

Question 31Matter, Energy, and Measurement

A 5.00 g sample of a solid is heated and completely melts at its melting point. During melting, the temperature of the sample remains constant even though heat is being added. Which statement explains this observation?

  1. The added heat is stored entirely as kinetic energy of the particles.
  2. The added heat is used to overcome intermolecular forces as the solid changes to a liquid. Correct answer.
  3. The heat is converted into chemical energy within the particles.
  4. The sample is losing heat to the surroundings at the same rate it gains heat.

Explanation

During a phase change, added energy increases the potential energy of the particles rather than their average kinetic energy. This energy breaks the forces holding particles in fixed positions, so the temperature does not change. Temperature is a measure of average kinetic energy, which stays constant during melting.

Question 32Matter, Energy, and Measurement

Which statement correctly distinguishes heat from temperature?

  1. Heat is a measure of average kinetic energy, while temperature is the total energy transferred.
  2. Heat and temperature are both measured in joules and mean the same thing.
  3. Temperature is a measure of average kinetic energy, while heat is energy transferred due to a temperature difference. Correct answer.
  4. Temperature depends on the amount of substance, while heat does not.

Explanation

Temperature reflects the average kinetic energy of the particles in a sample, while heat is the energy that flows from a warmer object to a cooler one. Heat depends on the mass and specific heat of the sample as well as the temperature change. This is why a large cool object can contain more thermal energy than a small hot one.

Question 33Matter, Energy, and Measurement

A sample of gas is held at constant volume while its temperature is lowered from 400 K to 200 K. Which statement describes what happens to the gas pressure?

  1. The pressure is halved because the average kinetic energy of the particles decreases. Correct answer.
  2. The pressure stays the same because the volume is unchanged.
  3. The pressure is quartered because the volume also decreases.
  4. The pressure doubles because the particles move faster.

Explanation

At constant volume, pressure is directly proportional to Kelvin temperature (Gay-Lussac's law). Halving the temperature from 400 K to 200 K halves the pressure, because the particles strike the walls less often and with less force. The volume is explicitly held constant.

Question 34Matter, Energy, and Measurement

A sample of gas has a pressure of 120 kPa at 300 K. If the temperature is raised to 450 K at constant volume, what is the new pressure?

  1. 180 kPa Correct answer.
  2. 240 kPa
  3. 80 kPa
  4. 90 kPa

Explanation

At constant volume, P1/T1 = P2/T2, so P2 = P1 × T2/T1 = 120 kPa × 450 K ÷ 300 K = 180 kPa. Because the absolute temperature increases by a factor of 1.5, the pressure rises by the same factor.

Question 35Matter, Energy, and Measurement

A 2.0 mol sample of an ideal gas occupies 44.8 L at standard temperature and pressure (0 °C and 1 atm). What volume would 0.50 mol of the same gas occupy at STP?

  1. 5.6 L
  2. 11.2 L Correct answer.
  3. 44.8 L
  4. 22.4 L

Explanation

At STP, one mole of any ideal gas occupies 22.4 L, so 0.50 mol occupies 0.50 × 22.4 L = 11.2 L. The volume is directly proportional to the number of moles at constant temperature and pressure.

Question 36Matter, Energy, and Measurement

A compound is analyzed and found to contain 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is its empirical formula?

  1. C2H6O
  2. C2H4O2
  3. CHO
  4. CH2O Correct answer.

Explanation

Assuming 100 g of compound gives 40.0 g C, 6.7 g H, and 53.3 g O. Dividing each by its molar mass gives 3.33 mol C, 6.7 mol H, and 3.33 mol O; dividing by the smallest gives the ratio 1:2:1, so the empirical formula is CH2O.

Question 37Matter, Energy, and Measurement

A hydrate of copper(II) sulfate, CuSO4·xH2O, has a molar mass of 249.7 g/mol. Given that anhydrous CuSO4 has a molar mass of 159.6 g/mol and water has a molar mass of 18.0 g/mol, what is the value of x?

  1. 7
  2. 3
  3. 10
  4. 5 Correct answer.

Explanation

The mass of water in one mole of the hydrate is 249.7 g − 159.6 g = 90.1 g. Dividing by the molar mass of water gives x = 90.1 ÷ 18.0 ≈ 5, so the formula is CuSO4·5H2O.

Question 38Matter, Energy, and Measurement

Which property of a substance is classified as a chemical property rather than a physical property?

  1. Its melting point
  2. Its ability to react with oxygen to form a new substance Correct answer.
  3. Its density at 20 °C
  4. Its solubility in water

Explanation

A chemical property describes how a substance reacts to form a new substance, such as its reactivity with oxygen. Physical properties, including density, melting point, and solubility, can be observed without changing the identity of the substance.

Question 39Matter, Energy, and Measurement

A 10.0 g sample of ice at 0 °C absorbs 3340 J of heat and melts completely at 0 °C. The heat of fusion of water is 334 J/g. What mass of ice remains unmelted if only 1670 J of heat is supplied to a 10.0 g sample at 0 °C?

  1. 2.5 g
  2. 0 g
  3. 5.0 g Correct answer.
  4. 7.5 g

Explanation

The heat needed to melt 1 g of ice is 334 J, so 1670 J can melt 1670 ÷ 334 = 5.0 g of ice. Starting with 10.0 g, 5.0 g melts and 5.0 g remains unmelted.

Question 40Matter, Energy, and Measurement

Two samples of different substances, each 50.0 g, absorb the same amount of heat. The specific heat of substance A is 0.50 J/(g·°C) and that of substance B is 2.0 J/(g·°C). Which statement correctly compares their temperature changes?

  1. Substance A warms four times as much as substance B. Correct answer.
  2. Substance B warms four times as much as substance A.
  3. Substance A warms twice as much as substance B.
  4. Both substances warm by the same amount.

Explanation

For equal masses and equal heat absorbed, the temperature change is inversely proportional to specific heat (ΔT = q/(m·c)). Since A has one quarter the specific heat of B, A warms four times as much as B.

Question 41Atomic Concepts and the Periodic Table

Which subatomic particle determines the identity of an element?

  1. The positron
  2. The proton Correct answer.
  3. The neutron
  4. The electron

Explanation

The atomic number equals the number of protons in the nucleus, and that number uniquely identifies an element on the periodic table. Changing proton count changes the element; changing neutron or electron count does not.

Question 42Atomic Concepts and the Periodic Table

An atom of an isotope has atomic number 17 and mass number 37. How many neutrons are in its nucleus?

  1. 17
  2. 20 Correct answer.
  3. 37
  4. 54

Explanation

The mass number is the sum of protons and neutrons, while the atomic number equals the proton count. Subtracting 17 protons from 37 nucleons leaves 20 neutrons.

Question 43Atomic Concepts and the Periodic Table

Which electron configuration represents an atom in an excited state?

  1. 1s² 2s² 2p⁶ 3s² 3p⁶
  2. 1s² 2s² 2p⁶ 3s¹
  3. 1s² 2s² 2p⁵ 3s¹ Correct answer.
  4. 1s² 2s² 2p⁶

Explanation

An excited state has an electron promoted into a higher subshell, leaving a lower subshell partially empty. The configuration 1s² 2s² 2p⁵ 3s¹ skips the normal filling of 2p before placing an electron in 3s.

Question 44Atomic Concepts and the Periodic Table

According to the modern wave-mechanical model, an orbital is best described as

  1. a region where the probability of finding an electron is high Correct answer.
  2. a fixed shell containing exactly eight electrons
  3. a positively charged region inside the nucleus
  4. a circular path followed by an electron around the nucleus

Explanation

The wave-mechanical model treats electrons as probability distributions rather than definite paths. An orbital is a three-dimensional region where finding an electron is most probable.

Question 45Atomic Concepts and the Periodic Table

Which statement correctly describes the emission spectrum of a hydrogen atom?

  1. It consists of dark lines produced when electrons absorb energy and rise to higher levels
  2. It consists of bright lines at specific wavelengths produced when electrons fall to lower energy levels Correct answer.
  3. It is identical to the absorption spectrum of hydrogen at every wavelength
  4. It is continuous because hydrogen emits all wavelengths of light

Explanation

Excited electrons release energy as photons of fixed energy when they drop to lower levels, giving bright lines at specific wavelengths. Each line corresponds to the energy difference between two levels.

Question 46Atomic Concepts and the Periodic Table

How many valence electrons does a neutral atom of phosphorus (atomic number 15) have?

  1. 5 Correct answer.
  2. 15
  3. 3
  4. 2

Explanation

Phosphorus has the configuration 1s² 2s² 2p⁶ 3s² 3p³, so its third shell holds five electrons. Those five electrons in the n = 3 shell are the valence electrons.

Question 47Atomic Concepts and the Periodic Table

Which element has the largest atomic radius?

  1. Potassium
  2. Lithium
  3. Sodium
  4. Rubidium Correct answer.

Explanation

Atomic radius increases down a group because each period adds a principal energy level farther from the nucleus. Rubidium lies lowest among these Group 1 metals, so it has the largest radius.

Question 48Atomic Concepts and the Periodic Table

Which property generally increases from left to right across a period on the periodic table?

  1. Metallic character
  2. Electronegativity Correct answer.
  3. Number of energy levels
  4. Atomic radius

Explanation

Across a period, increasing nuclear charge pulls valence electrons more strongly, so electronegativity rises. Atomic radius and metallic character decrease in the same direction.

Question 49Atomic Concepts and the Periodic Table

Which pair of elements has the most similar chemical properties?

  1. Cl and Ar
  2. Ca and Sr Correct answer.
  3. O and S
  4. Na and Mg

Explanation

Calcium and strontium are both Group 2 alkaline earth metals, so they share valence electron counts and similar reactivity. Elements in the same group have the most similar chemistry.

Question 50Atomic Concepts and the Periodic Table

Which element is classified as a metalloid?

  1. Argon
  2. Sulfur
  3. Aluminum
  4. Silicon Correct answer.

Explanation

Metalloids border the staircase line on the periodic table and show mixed metal and nonmetal properties. Silicon lies along that line and is the standard metalloid example.