Atoms and Molecules Practice Questions
20 free Atoms and Molecules practice questions for the Static GK. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which subatomic particle was discovered by J.J. Thomson using the cathode ray tube experiment?
- A Proton
- B Neutron
- C Electron
- D Positron
Correct answer: Electron
J.J. Thomson discovered the electron in 1897. His experiment showed that cathode rays were composed of previously unknown negatively charged particles, which were later named electrons.
What is the name of the central part of an atom that contains protons and neutrons?
- A Orbit
- B Valence shell
- C Isotope
- D Nucleus
Correct answer: Nucleus
The nucleus is the small, dense region at the center of an atom. It was discovered by Ernest Rutherford through his famous gold foil experiment in 1911.
The total number of protons and neutrons in the nucleus of an atom is known as its:
- A Atomic number
- B Mass number
- C Isotopic ratio
- D Valency
Correct answer: Mass number
The mass number (A) is the sum of protons and neutrons in an atom's nucleus. It is distinct from the atomic number, which represents only the number of protons.
Atoms of the same element that have the same number of protons but different numbers of neutrons are called:
- A Isotopes
- B Isobars
- C Isotones
- D Isomers
Correct answer: Isotopes
Isotopes are variants of a particular chemical element which differ in neutron number. For example, Carbon-12 and Carbon-14 are isotopes of carbon.
Which of the following laws states that 'Mass can neither be created nor destroyed in a chemical reaction'?
- A Law of Constant Proportions
- B Law of Multiple Proportions
- C Avogadro's Law
- D Law of Conservation of Mass
Correct answer: Law of Conservation of Mass
The Law of Conservation of Mass was established by Antoine Lavoisier. It implies that the total mass of reactants must equal the total mass of products in a closed system.
What is the value of Avogadro's constant ($N_A$)?
- A 6.022 × 10^23 per mole
- B 1.602 × 10^-19 per mole
- C 9.109 × 10^-31 per mole
- D 3.141 × 10^23 per mole
Correct answer: 6.022 × 10^23 per mole
Avogadro's constant represents the number of constituent particles (usually atoms or molecules) in one mole of a substance. It is approximately 6.02214076 × 10^23.
The combining capacity of an atom of an element is known as its:
- A Charge
- B Electronegativity
- C Ionization potential
- D Valency
Correct answer: Valency
Valency is determined by the number of electrons in the outermost shell of an atom. It dictates how many chemical bonds an atom can form with other atoms.
Who proposed the first modern atomic theory, suggesting that atoms are indivisible and indestructible?
- A Niels Bohr
- B John Dalton
- C Robert Boyle
- D James Chadwick
Correct answer: John Dalton
John Dalton published his atomic theory in 1808. Although we now know atoms can be divided into subatomic particles, his work laid the foundation for modern chemistry.
Which subatomic particle has no electrical charge?
- A Proton
- B Electron
- C Alpha particle
- D Neutron
Correct answer: Neutron
The neutron is a neutral particle found in the nucleus. It was discovered by James Chadwick in 1932.
What is the maximum number of electrons that can be accommodated in the 'K' shell of an atom?
- A 2
- B 8
- C 18
- D 32
Correct answer: 2
According to the $2n^2$ rule, the first shell (K shell, where $n=1$) can hold a maximum of 2 electrons. The subsequent L shell ($n=2$) can hold 8.
The smallest unit of a compound that maintains the chemical properties of that compound is a/an:
- A Atom
- B Ion Pair
- C Element
- D Molecule
Correct answer: Molecule
A molecule is a group of two or more atoms chemically bonded together. While atoms are the smallest unit of an element, molecules are the smallest units of compounds.
Which of these elements is 'polyatomic' in its natural molecular form?
- A Helium
- B Oxygen
- C Nitrogen
- D Sulfur
Correct answer: Sulfur
Sulfur typically exists as $S_8$ molecules, making it polyatomic. Oxygen and Nitrogen are diatomic ($O_2, N_2$), while Helium is monatomic.
What is the mass of one mole of a substance called?
- A Molar mass
- B Molecular weight
- C Equivalent weight
- D Molality
Correct answer: Molar mass
Molar mass is the mass of a given substance divided by the amount of that substance in moles. It is numerically equal to the atomic or molecular mass but expressed in g/mol.
Which subatomic particle determines the 'Atomic Number' of an element?
- A Proton
- B Neutron
- C Electron
- D Meson
Correct answer: Proton
The atomic number is defined as the number of protons in the nucleus of an atom. This number is unique to each element and determines its position in the Periodic Table.
An atom that has gained or lost electrons and carries an electrical charge is called a/an:
- A Isotope
- B Isomer
- C Ion
- D Nucleon
Correct answer: Ion
Ions are charged particles. A positively charged ion is called a cation (lost electrons), and a negatively charged ion is called an anion (gained electrons).
The Law of Definite Proportions (or Constant Proportions) was given by:
- A Joseph Proust
- B John Dalton
- C Antoine Lavoisier
- D Joseph Louis Gay-Lussac
Correct answer: Joseph Proust
Joseph Proust stated that a chemical compound always contains exactly the same proportion of elements by mass. For example, water always contains hydrogen and oxygen in a 1:8 mass ratio.
Which atomic model is often referred to as the 'Plum Pudding Model'?
- A Rutherford's Model
- B Bohr's Model
- C Thomson's Model
- D Dalton's Model
Correct answer: Thomson's Model
Thomson's model suggested that an atom is a sphere of positive charge with electrons embedded in it like raisins in a pudding. This was later disproved by Rutherford.
What is the atomic mass unit (amu or u) currently based on?
- A 1/16th mass of an Oxygen-16 atom
- B 1/12th mass of a Carbon-12 atom
- C Mass of a Hydrogen-1 atom
- D 1/14th mass of a Nitrogen-14 atom
Correct answer: 1/12th mass of a Carbon-12 atom
The unified atomic mass unit is defined as exactly 1/12th of the mass of an unbound neutral atom of carbon-12 at rest and in its ground state.
How many atoms are present in a molecule of Ozone?
- A 1
- B 2
- C 3
- D 4
Correct answer: 3
Ozone is a triatomic molecule consisting of three oxygen atoms ($O_3$). It is an allotrope of oxygen that is much less stable than the diatomic $O_2$.
Which experiment proved that most of the space inside an atom is empty?
- A Millikan's oil drop experiment
- B J.J. Thomson's cathode ray experiment
- C Alpha-particle scattering experiment
- D Photoelectric effect experiment
Correct answer: Alpha-particle scattering experiment
In Rutherford's alpha-particle scattering experiment, most particles passed through the gold foil without deflection. This proved that the vast majority of an atom's volume is empty space.