HESI A2 Elsevier (HESI): HESI Admission Assessment - Set 5 - Part 1

Correct Answer: Expresses very large or small numbers

Scientific notation expresses very large or very small values compactly using a coefficient and a power of ten. This system simplifies calculations and reduces writing errors during careful scientific work and study. Option a is incorrect because Converting between temperature scales uses formulas relating Celsius, Fahrenheit, and Kelvin to one another. This task is unrelated to the compact notation system used to write extreme magnitudes simply in science. Option b is incorrect because Balancing equations applies the conservation of mass by adjusting coefficients carefully. This task is separate from the notation system used to write extreme numerical magnitudes in compact form during scientific work. Option d is incorrect because Ionic charge is determined by electron gain or loss based on group position on the periodic table. This determination has nothing to do with any system used to compact the writing of numerical magnitudes.

Correct Answer: Gram

The gram and its prefixed forms such as kilogram and milligram are the metric base units used for measuring mass. They appear widely in chemistry, medicine, nursing practice, and laboratory settings. Option b is incorrect because The liter measures volume, which is the amount of space occupied by a substance, rather than mass. Mass is the property representing the quantity of matter contained within an object or sample. Option c is incorrect because The meter measures length or distance between two points in space, not mass at all. Mass is the property describing the amount of matter present in any object or chemical sample being measured. Option d is incorrect because The second measures time intervals during which events occur in physics and chemistry. It is unrelated to mass, the physical property describing how much matter an object actually contains in its structure.

Correct Answer: Kelvin

Kelvin sets its zero point at absolute zero, the theoretical limit where particle motion stops entirely. This anchoring makes Kelvin the standard scientific scale used universally throughout chemistry and physics work today. Option a is incorrect because Celsius places its zero point at the freezing point of water, well above absolute zero. The scale includes negative values for cold conditions and is therefore not anchored at the lowest possible temperature limit. Option b is incorrect because Fahrenheit places its zero on a historical brine reference point and allows many negative values for cold conditions. It is not anchored to absolute zero, the theoretical minimum temperature in physical reality. Option c is incorrect because Rankine is also anchored to absolute zero in physics, but the question asks for the standard scientific scale. Kelvin is the universally accepted answer used throughout chemistry and physics by scientists everywhere today.

Correct Answer: Converts between units using factors

Dimensional analysis converts quantities between units by multiplying by ratios that equal one. This procedure allows units to cancel correctly so only the desired unit remains in the final answer for the calculation. Option a is incorrect because Predicting reaction products requires knowledge of reactivity, periodic trends, and reaction types in chemistry. None of these skills are part of unit conversion using ratio based factors that cancel and produce a desired unit. Option c is incorrect because Balancing redox half reactions involves equalizing electrons gained and lost between species during the reaction. This task is unrelated to converting measured quantities from one set of units to another using ratio based factors. Option d is incorrect because Spectral identification matches emission lines to characteristic patterns of elements in atomic physics. This technique has nothing to do with converting between metric or imperial units using factors set equal to one in chemistry.

Correct Answer: Kilo means thousand times the base

Kilo means one thousand times the base unit during measurement. So a kilogram represents a thousand grams and a kilometer represents a thousand meters, used commonly in scientific measurement work everywhere today in science. Option a is incorrect because Milli denotes a value much smaller than the base unit, not larger as the option claims. The prefix represents one thousandth of the base rather than a thousandfold multiplication of the base unit during measurement. Option b is incorrect because Centi represents one hundredth of the base unit during measurement. This indicates a smaller fraction rather than a multiplier that makes the unit larger by any factor of ten during scientific measurement work. Option d is incorrect because Mega indicates a million times the base unit during measurement, which makes any quantity much larger rather than smaller. The prefix is widely used for very large measurements like megawatts or megahertz in physics.

Correct Answer: Proton

The proton count, called the atomic number, defines the identity of an element on the periodic table. Changing the proton number changes the element entirely, while neutron or electron changes do not affect element identity. Option b is incorrect because Neutrons affect the mass number and create isotopes of the same element. They do not determine which element an atom represents on the periodic table, since isotopes of an element share the same identity. Option c is incorrect because Electrons determine charge and chemical behavior of an atom in reactions. Losing or gaining electrons forms ions of the same element rather than producing a different element altogether on the modern periodic table. Option d is incorrect because Positrons are antiparticles of electrons that appear in certain nuclear processes inside special reactions. They are not stable components of ordinary atoms, so they have no role in defining the identity of any element.

Correct Answer: Increasing atomic number

The modern periodic table arranges elements by increasing atomic number, which equals the proton count. This arrangement reveals the periodic recurrence of chemical and physical properties throughout the entire table for chemists worldwide. Option a is incorrect because Density does not increase regularly across the periodic table from one end to the other. Elements are not arranged by density at all, since density depends on atomic packing in ways that vary irregularly. Option b is incorrect because Alphabetical ordering would scatter related elements throughout the table without regard to chemical behavior. This arrangement would fail to reveal the recurring chemical patterns that the periodic arrangement is designed to display. Option c is incorrect because Order of discovery reflects history rather than chemical behavior of the elements involved. The periodic table is built around recurring properties, which are revealed only by an arrangement based on increasing atomic number.

Correct Answer: Same element with different neutron count

Isotopes share the same proton number, which makes them the same element on the periodic table. They differ in neutron count, which causes them to have different mass numbers but very similar chemical behavior. Option a is incorrect because Atoms that gain or lose electrons are called ions and carry net positive or negative charges in solution. They are not isotopes, which involve nuclear differences rather than changes in the surrounding electron cloud structure. Option c is incorrect because Atoms with different proton counts represent different elements rather than isotopes of one element. Isotopes share the proton number and element identity, but vary in neutron count and therefore in atomic mass numbers. Option d is incorrect because Molecules with rearranged bonds are called isomers, which are different structural forms of the same molecular formula. This term does not apply at the atomic nucleus level the way the term isotope does in chemistry.

Correct Answer: Covalent bond

Covalent bonds form when atoms share one or more pairs of electrons between them in a molecule. This sharing allows each atom to achieve a stable outer electron configuration without transferring electrons completely between atoms. Option a is incorrect because Ionic bonds form when electrons transfer from one atom to another, which creates oppositely charged ions that attract. Ionic bonds do not involve any mutual sharing of electron pairs between bonded atoms in a molecule. Option b is incorrect because Hydrogen bonds are weak intermolecular attractions between polar molecules in solution or in pure substances. They are not true chemical bonds formed by the mutual sharing of electron pairs between two atoms in chemistry. Option d is incorrect because Metallic bonds involve a sea of delocalized electrons shared among many metal atoms throughout the lattice. This differs fundamentally from the discrete electron pair sharing between two specific atoms that defines covalent bonding in ch

Correct Answer: Halogens

Halogens have seven valence electrons and gain one electron easily to complete their outer shell. This behavior makes them highly reactive nonmetals that readily form negatively charged ions during reactions with metals in chemistry. Option b is incorrect because Alkali metals are highly reactive metals that lose one electron to achieve stability in chemical reactions. They form positive ions rather than gaining an electron the way nonmetal halogens do during ionic bond formation. Option c is incorrect because Noble gases already have full outer electron shells in their natural state. This electron arrangement makes them generally unreactive and unwilling to gain or lose electrons under normal chemical conditions encountered in the laboratory. Option d is incorrect because Transition metals are metals with variable oxidation states across the middle of the periodic table. They typically lose electrons to form positive ions instead of gaining electrons the way halogens behave during ion

Correct Answer: Each element appears equally on both sides

A balanced equation has equal numbers of each element on both sides of the equation arrow. This balance reflects the conservation of mass, since coefficients ensure that no atoms are lost or gained. Option a is incorrect because Color is a physical property that may or may not change during a chemical reaction in the lab. Color has nothing to do with whether atoms are conserved across the equation arrow itself. Option b is incorrect because Coefficients are adjusted as needed to balance an equation in chemistry. Many properly balanced equations contain coefficients greater than one, so equal coefficients are not required for an equation to be considered balanced. Option c is incorrect because Counts of reactant and product species do not need any particular relationship in number. Balance requires only that atoms of each element appear in equal numbers on both sides of the equation arrow itself.

Correct Answer: Synthesis

A synthesis or combination reaction occurs when two or more reactants join together to produce a single, more complex product. Elements often combine directly to form a compound during this type of chemical change. Option a is incorrect because Decomposition is the opposite type of reaction, where one compound breaks apart into two or more simpler products. The breakdown is usually driven by heat, light, or electrical input, rather than combining several reactants together. Option c is incorrect because Single replacement involves one element displacing another from within a compound during the reaction. This produces a new element and a new compound rather than joining several reactants together into one combined product. Option d is incorrect because Double replacement involves an exchange of ions between two compounds during the reaction in solution. This generates two new compounds rather than combining all of the reactants into a single product during the chemical change.

Correct Answer: Exothermic

Exothermic reactions release heat to the surroundings during the reaction, which is often felt as warmth. Combustion and many neutralization reactions are common examples of exothermic processes that warm their environment as products form. Option b is incorrect because Endothermic reactions absorb heat from the surroundings rather than releasing it during the reaction. They often produce a cooling effect at the reaction site as the chemical reaction proceeds toward forming new products in solution. Option c is incorrect because Photochemical reactions absorb light energy to drive the process forward in the lab. They may release or absorb heat depending on the reaction itself, since the defining feature is light absorption rather than heat release. Option d is incorrect because Reversibility refers to whether a reaction can proceed in both directions during equilibrium. This concept does not specify any particular heat behavior, since reversible reactions can be either exothermic or en

Correct Answer: A compound breaks into simpler substances

A decomposition reaction starts with a single compound that breaks apart into two or more simpler substances. This breakdown is often driven by heat, light, or an electric current applied externally to the original compound. Option a is incorrect because Ion exchange between two compounds describes a double replacement reaction, not decomposition. Decomposition involves a single starting compound breaking apart rather than two compounds reacting together and trading ions during the chemical change. Option b is incorrect because Replacement of one element by another within a compound describes a single replacement reaction. Decomposition starts with one compound breaking apart, not with one element reacting with a compound to displace another element. Option d is incorrect because Combination of two reactants into one product describes synthesis, the opposite of decomposition. Decomposition begins with one substance and produces multiple simpler products rather than combining several in

Correct Answer: Total mass of reactants equals products

Conservation of mass requires that the total mass of reactants equals the total mass of products. Atoms are neither created nor destroyed but simply rearranged into new substances during a chemical reaction. Option a is incorrect because Temperature can change during a reaction without violating the conservation of mass principle in chemistry. Mass conservation depends on equal atom counts across the equation, not on any matching of temperatures between sides. Option b is incorrect because Reactions can occur in any phase, including solid, liquid, or gas, without affecting mass conservation. The principle requires equal mass on both sides of the chemical equation throughout the chemical change in any phase. Option c is incorrect because Heat release relates to energy changes during the reaction, not to mass conservation principles. Both endothermic and exothermic reactions equally obey the principle that mass is neither created nor destroyed during a chemical change.

Correct Answer: Raising the temperature

Raising temperature gives particles more kinetic energy, which leads to more frequent and more energetic collisions. This increases the fraction of effective collisions and speeds up the rate at which products form during the reaction. Option a is incorrect because Lowering temperature reduces particle kinetic energy, which decreases the frequency and force of collisions between molecules. This produces a slower reaction rate rather than increasing the rate at which the reaction proceeds toward products. Option c is incorrect because Reducing surface area means that fewer particles of the solid reactant are exposed to react at any moment. Smaller surface area decreases collision opportunities and lowers the rate of a heterogeneous chemical reaction overall. Option d is incorrect because Removing a catalyst eliminates the alternative lower energy pathway it provides for the reaction. This slows the reaction rather than speeding it up, since catalysts increase reaction rate without being

Correct Answer: The system shifts to relieve stress

Le Chatelier's principle states that a system at equilibrium shifts in the direction that relieves the applied stress. This shift restores a new equilibrium state under the changed conditions of concentration, pressure, or temperature. Option a is incorrect because Equilibrium is dynamic rather than static, and any stress applied to the system causes a shift in position. Forward and reverse reactions continue at adjusted rates rather than stopping permanently when a stress appears. Option b is incorrect because Forward and reverse reactions never both stop at equilibrium during normal operation. They continue at equal rates during equilibrium, and a stress simply shifts which direction temporarily dominates until balance is restored under new conditions. Option d is incorrect because The forward direction does not always prevail when stress is applied to an equilibrium system. The direction of the shift depends on the type of stress applied, since changes can favor either side.

Correct Answer: Holds maximum solute at that temperature

A saturated solution holds the maximum amount of dissolved solute at a given temperature in equilibrium with any undissolved solid present. Adding more solute will not dissolve and instead settles to the bottom. Option b is incorrect because A solution by definition requires a solvent to dissolve the solute particles. Without a solvent no solution exists at all, so the absence of solvent does not describe any kind of solution. Option c is incorrect because A solution containing less solute than the maximum is called unsaturated rather than saturated in chemistry. An unsaturated solution can still dissolve more solute, since it has not reached its full capacity yet. Option d is incorrect because Electrical conductivity depends on whether the dissolved solute produces ions in solution, not on saturation status. Saturated solutions of nonelectrolytes such as sugar do not conduct electricity well at all under normal conditions.

Correct Answer: Increasing temperature

Increasing temperature usually increases the solubility of solid solutes in liquid solvents during normal heating. The added thermal energy helps disrupt the solid lattice and allows more particles to enter solution and stay dissolved. Option a is incorrect because Removing solute does not change solubility, which is the maximum amount of solute that can dissolve. The action simply leaves the solvent less concentrated, while the actual dissolving capacity of the solvent stays unchanged. Option b is incorrect because Pressure has very little effect on the solubility of solids in liquids during normal conditions. Pressure changes mainly affect the solubility of gases in liquids, where higher pressure increases the dissolved gas amount in solution. Option c is incorrect because Adding more solid does not raise solubility itself in any way. If the solution is already saturated at the current temperature, the extra solid simply remains undissolved at the bottom of the container.

Correct Answer: Shifts toward the products

Adding more reactant pushes the equilibrium forward, which shifts it toward products to consume the added substance. This shift restores balance under the new conditions of concentration in the chemical system overall. Option a is incorrect because Adding reactants does not cause the system to consume what is already there in a way that ignores the new addition. The system uses the added reactant to form more products and restore balance. Option b is incorrect because Equilibrium systems always respond to applied stresses according to Le Chatelier's principle in chemistry. They never become unresponsive to changes in concentration, temperature, or pressure that are applied to the chemical system overall. Option d is incorrect because The system would not move backward to make more of the substance just added to the system. That action would worsen the imbalance instead of relieving the stress applied to the system as a whole.