Atomic Structure — Set 3
Chemistry · परमाणु संरचना · Questions 21–30 of 50
What is the shape of an 's' orbital?
Correct Answer: A. Spherical
• **Spherical shape** = Electron probability cloud symmetrical about nucleus; equal probability in all directions. • **l=0 for s-orbital** — All s orbitals (1s, 2s, 3s) spherical but increasing radius as n increases. • 💡 Wrong-option analysis: B: Double dumbbell is d-orbital shape; C: Circular is 2D not 3D shape description; D: Single dumbbell is p-orbital shape.
Which fundamental force holds the protons and neutrons together in the nucleus?
Correct Answer: C. Strong nuclear force
• **Strong nuclear force** = Most powerful force nature; overcomes proton-proton electromagnetic repulsion in nucleus. • **Short-range only** — Acts within 1-3 femtometers; rapidly weakens with distance, does not extend beyond nucleus. • 💡 Wrong-option analysis: A: Weak force causes radioactive decay, not nuclear binding; B: Electromagnetic repels same charges; D: Gravity too weak to bind nuclei.
An atom that has gained or lost electrons and carries a charge is called a/an?
Correct Answer: A. Ion
• **Ion definition** = Charged atom formed by losing (cation: +) or gaining (anion: −) electrons. • **Unequal protons/electrons** — More protons than electrons = positive; more electrons than protons = negative. • 💡 Wrong-option analysis: B: Molecule is combination of atoms bonded together; C: Radical has unpaired electron but may be neutral; D: Isotope refers to neutron variation not electron loss/gain.
What is the maximum number of electrons that can fit into a 'p' subshell?
Correct Answer: C. 6
• **p subshell = 3 orbitals** = Three p orbitals (p_x, p_y, p_z) each holding maximum 2 electrons. • **Total = 6 electrons** — 3 orbitals × 2 electrons per orbital = 6 electrons maximum capacity. • 💡 Wrong-option analysis: A: 2 electrons is capacity of s subshell only; B: 10 electrons is d subshell capacity; D: 14 electrons is f subshell capacity.
Which model of the atom is often referred to as the 'Planetary Model'?
Correct Answer: C. Bohr's Model
• **Bohr's Model (1913)** = Electrons orbit nucleus in fixed circular orbits like planets around sun; quantized energy levels. • **Explained hydrogen spectrum** — Successfully predicted hydrogen spectral lines using Planck's quantization concept. • 💡 Wrong-option analysis: A: Thomson's model had atoms as pudding; B: Quantum model uses probability clouds not orbits; D: Dalton's model just indivisible spheres with no internal structure.
What is the mass of a neutron relative to an atomic mass unit (amu)?
Correct Answer: B. 1
• **Neutron mass = 1.0087 amu** ≈ 1 amu; essentially same as proton mass. • **Nucleon mass unit** — Both neutrons and protons weigh about 1 amu, so mass number counts them together. • 💡 Wrong-option analysis: A: 0.5 amu is electron mass relative value, not neutron; C: 2 amu is too heavy; D: 0 amu would mean no mass, but neutron has measurable mass.
Which element has only one proton and no neutrons in its most common isotope?
Correct Answer: B. Hydrogen
• **Protium (^1H)** = Most abundant hydrogen isotope with 1 proton, 0 neutrons, 1 electron only. • **Simplest atom** — The only nucleus consisting of single proton; all others have multiple nucleons. • 💡 Wrong-option analysis: A: Beryllium has 4 protons and 5 neutrons minimum; C: Lithium has 3 protons and 4 neutrons; D: Helium has 2 protons and 2 neutrons.
The arrangement of electrons in the various shells of an atom is known as?
Correct Answer: A. Electronic configuration
• **Electronic configuration** = Notation showing how electrons distributed in shells and subshells; example 1s^2 2s^2 2p^6. • **Determines chemistry** — Electronic configuration uniquely determines how atom bonds and chemical behavior. • 💡 Wrong-option analysis: B: Atomic structure includes nucleus and overall atom layout; C: Molecular geometry describes molecular shape not electron arrangement; D: Quantum state refers to single electron state not full configuration.
Which type of radiation has the highest penetrating power?
Correct Answer: C. Gamma rays
• **Gamma rays (γ)** = High-energy electromagnetic radiation with no mass/charge; travels at light speed. • **Highest penetrating power** — No charge means no electrical interaction; requires thick lead or concrete shielding. • 💡 Wrong-option analysis: A: Alpha rays are heavy helium nuclei, stopped by paper; B: Beta rays are electrons, stopped by aluminum; D: X-rays penetrate less than gamma rays.
What is the value of the charge on a single electron?
Correct Answer: B. -1.6 × 10^-19 Coulombs
• **Elementary charge magnitude** = 1.6 × 10^-19 coulombs (Faraday's constant basis). • **Negative sign** — Electron carries negative charge; denoted -1.6 × 10^-19 C (negative of elementary charge). • 💡 Wrong-option analysis: A: Exponent -23 is wrong magnitude; C: Negative sign correct but magnitude exponent wrong; D: Positive 1.6 × 10^-19 is proton charge not electron.