MCQ on Structure of Atom Class 10

Explanation: The question asks which element has an equal number of protons and neutrons, meaning its Atomic Structure is balanced.

Atoms are composed of protons, neutrons, and electrons. The atomic number gives the number of protons, and the Mass number represents the sum of protons and neutrons. To find neutrons, subtract the atomic number from the Mass number.

To solve this, examine each element and its isotope if provided. Calculate neutrons as: neutrons = Mass number − atomic number. Compare this with the number of protons. The element whose proton and neutron counts match satisfies the condition. For elements without explicit isotopes, standard atomic data can be used. Systematically checking each option ensures a logical choice.

Imagine protons and neutrons as equal teams on a balance scale; when numbers match, the system is stable.

In short, by comparing proton and neutron counts using atomic and Mass numbers, one can identify the Atom with equal numbers of both.

Explanation: This question examines why electrons are termed universal due to their consistent properties regardless of their source.

Electrons are fundamental particles present in all atoms. Their charge and Mass are constant, as confirmed by experiments such as cathode ray studies. These experiments show that electrons behave identically irrespective of the material or gas used.

In discharge tube experiments, cathode rays are produced by passing Electricity through gases. The rays’ behavior and charge-to-Mass ratio remain the same across all materials. This shows that electrons are identical everywhere. Since electrons exist in all atoms and exhibit uniform properties, they are called universal. Repeated experimental observations reinforce this conclusion.

Think of it like identical Light bulbs from different manufacturers—though sourced differently, they behave exactly the same when powered.

In short, electrons are universal because their properties remain unchanged across all atoms and materials.

Explanation: This question asks to identify statements that do not align with known characteristics of cathode rays, based on experimental evidence.

Cathode rays are streams of electrons observed in vacuum discharge tubes. They have Mass, carry negative charge, and move in straight lines. They can rotate a Light paddle wheel, deflect under electric and magnetic fields, and ionize gases.

To evaluate statements, compare each option with established properties. Any statement that claims cathode rays are unaffected by electric/magnetic fields, or are not material particles, contradicts experimental findings. Understanding the behavior of cathode rays in vacuum tubes helps isolate inconsistencies.

Think of cathode rays like invisible bowling balls; they can push objects, respond to fields, and exist in all tubes. Any statement denying these behaviors would be contradictory.

In short, carefully compare each statement with known experimental properties of cathode rays to identify contradictions.

Explanation: This question focuses on identifying particles that have Mass and momentum sufficient to impart mechanical motion to a paddle wheel.

Experiments with cathode rays showed that certain subatomic particles can transfer momentum to small objects. Particles must have mass and move in a stream to physically rotate the wheel. Electrons, being the constituents of cathode rays, fulfill these criteria.

To reason, consider which particles in atoms are mobile and carry momentum. Protons and neutrons are within the nucleus and cannot move freely in the discharge tube. Electrons, however, move at high speeds and have measurable mass, which allows them to rotate the wheel.

An analogy is wind pushing a pinwheel—moving air molecules have mass and transfer momentum to rotate it. Electrons behave similarly in cathode ray experiments.

In short, the particles capable of physically rotating a Light paddle wheel are those that are mobile, have mass, and move as a stream.

Explanation: The question asks about the scientist who pioneered experiments using discharge tubes to study cathode rays.

Discharge tube experiments were designed to observe the behavior of electrons in vacuum tubes. Early experiments involved passing electric currents through gases at low pressure to produce cathode rays. Scientists studied their properties, such as motion, deflection, and interaction with Light paddle wheels.

To reason, consider historical timelines: the first observations of cathode rays were made by scientists investigating electrical conduction in gases. The experiment involved a vacuum tube with electrodes connected to a high-voltage source. The emitted rays revealed particles moving from cathode to anode, laying the foundation for later discoveries of electrons.

This is similar to noticing the first footprints on fresh snow—they indicate the earliest presence of activity in that area.

In short, the discharge tube experiment was first carried out to observe the behavior of cathode rays and study their physical properties.

Explanation: This question explores why the ratio of charge to mass of cathode ray particles remains constant across different experiments.

Cathode rays consist of electrons. Their charge (e) and mass (m) are intrinsic properties. Experiments consistently measured the ratio e/m for electrons in various gases and materials. The ratio remains constant because electrons are identical, regardless of the source.

To reason, consider multiple discharge tube experiments: rays produced in different conditions always gave the same deflection under electric/magnetic fields. Since the ratio of charge to mass determines behavior in fields, identical behavior across experiments implies a constant e/m. This uniformity demonstrates the universal nature of electrons.

Think of it as identical coins from different mints having the same weight-to-value ratio; behavior remains consistent.

In short, the charge-to-mass ratio of cathode rays is constant because the particles involved are identical and behave uniformly across all experimental conditions.

Explanation: This question asks what particles result when a neutron breaks down, based on nuclear decay processes.

A free neutron is unstable and undergoes beta decay. During this process, a neutron transforms into other subatomic particles. The decay follows conservation laws, including charge, energy, and momentum.

To reason, consider neutron decay in isolation: the neutron consists of quarks whose rearrangement produces a proton and emits an electron (beta particle) along with an antineutrino. This explains why neutron decay results in a particle transformation rather than simple disappearance. Understanding beta decay and conservation laws helps predict the outcome.

An analogy is a Lego piece being rearranged into new shapes; the original structure changes into distinct components without vanishing.

In short, neutron decay produces new particles following fundamental conservation laws, transforming the original particle into others while preserving energy and charge.

Explanation: The question asks for the electron capacity of the outermost shell (valence shell) of an Atom, based on electron configuration rules.

Electron shells are arranged in energy levels around the nucleus. The maximum number of electrons in a shell is determined by the formula 2n², where n is the shell number. The valence shell’s capacity governs chemical properties and Bonding behavior.

To reason, identify the outermost shell and apply the formula. For many atoms, especially in the first few periods, the outermost shell can accommodate up to 8 electrons (octet rule), though higher shells can hold more depending on quantum numbers. Understanding electron distribution helps predict Bonding and reactivity.

Think of it like seats in a bus row; each row has a fixed number of seats, and the outermost row can only hold so many passengers.

In short, the outermost electron shell has a limit based on quantum rules, which determines chemical behavior and Bonding potential.

Explanation: This question focuses on the major discovery made by E. Rutherford in Atomic Structure studies.

Rutherford conducted the gold foil experiment, sending alpha particles through thin metal sheets. Most particles passed through, but some deflected sharply, indicating a dense, positively charged nucleus.

To reason, consider the observations: the deflection of a small fraction of particles suggested that most of the Atom is empty space, with mass concentrated in the center. This overturned the earlier plum pudding model and introduced the nuclear model of the atom. Understanding experimental outcomes helps identify what Rutherford discovered.

It’s like tossing marbles at a balloon; most pass through the empty space, but a few hit a dense object inside, revealing its presence.

In short, Rutherford’s experiments revealed a dense central nucleus and mostly empty space around it, changing the atomic model fundamentally.

Explanation: This question asks which scientist suggested that electrons occupy specific energy levels, rather than moving arbitrarily around the nucleus.

Earlier models assumed electrons could have any energy while orbiting. Observations of atomic spectra showed discrete lines, implying electrons exist only in certain energy levels. This concept explained stability and emission/absorption patterns.

To reason, consider the behavior of electrons: energy changes occur only when electrons jump between fixed levels, emitting or absorbing photons. This model resolved inconsistencies in classical atomic theories and matched experimental spectral data. Understanding energy quantization explains the origin of spectral lines.

An analogy is stairs in a building: you cannot stand between steps; electrons occupy specific “steps” or energy levels.

In short, the idea of fixed energy levels explains why electrons remain in discrete orbits and why atoms emit specific spectral lines.

Explanation: This question asks for the particle that forms the nucleus of a hydrogen atom, the simplest atom in the Periodic Table.

Atoms consist of electrons orbiting a central nucleus, which contains protons and, in heavier atoms, neutrons. Hydrogen is unique because it has only one proton in its nucleus and typically no neutrons in its most common isotope.

To reason, consider the structure of hydrogen: the single proton carries a positive charge and constitutes the entire nucleus. Electrons orbit this proton, balancing the charge. This simplicity is why hydrogen is often used to explain atomic models and basic nuclear concepts.

Think of hydrogen as a tiny Solar system with only one sun (proton) and one planet (electron) orbiting it.

In short, the nucleus of a hydrogen atom consists of a single particle that carries a positive charge and defines the atom’s identity.

Explanation: The question focuses on identifying subatomic particles whose numbers are equal in a neutral atom, ensuring electrical neutrality.

Atoms contain protons (positively charged), electrons (negatively charged), and neutrons (neutral). In a neutral atom, the number of protons equals the number of electrons to balance the overall charge, while neutrons may vary depending on the isotope.

To reason, consider the neutrality condition: charge balance requires that total positive charge equals total negative charge. Since protons and electrons carry equal but opposite charges, they must be equal in number. Neutrons do not affect charge, so their number can differ. Understanding this principle is key to identifying the correct particle pair.

An analogy is a seesaw with equal weights on both sides; protons and electrons balance the atom just like the seesaw remains level.

In short, the number of protons and electrons is equal in a neutral atom to maintain electrical balance.

Explanation: This question asks which factor controls the total positive charge of an atom’s nucleus.

The nucleus contains protons (positive charge) and neutrons (neutral). The total positive charge depends entirely on the number of protons because each proton carries a single positive charge. Neutrons contribute mass but not charge.

To reason, examine the atomic number: it represents the number of protons in the nucleus. Therefore, the nuclear charge is directly determined by this number. Changes in electron count or Chemical Bonding do not affect the positive charge of the nucleus, which is fixed for each element.

Think of the nucleus as a SET of positively charged beads; the total positive charge equals the number of beads (protons) present.

In short, the number of protons in the nucleus determines its positive charge.

Explanation: This question asks to identify which atom has less than 8 electrons in its second shell (L-shell) based on electron configuration rules.

Electron shells fill according to the 2n² rule, where n is the shell number. The second shell (n=2) can hold up to 8 electrons. The electron configuration of an atom is determined by its atomic number, which equals the total number of electrons.

To reason, subtract electrons filling the first shell (2 electrons) from the total atomic number to find electrons in the second shell. Compare the count with 8 to see which atom has fewer. This helps predict valence electrons and chemical reactivity.

Think of filling a two-tier bus: the first tier takes 2 passengers, and the remaining go to the second tier. Some atoms may have fewer than the full capacity in the second tier.

In short, calculating electrons in the L-shell from the atomic number helps identify the atom with fewer than 8 electrons in that shell.