CBSE Class 9 Science Chapter 08 Journey Inside The Atom MCQs Set 01

Answer: (A) Parmanus

Explanation:
Kanada called the smallest, senses-imperceptible units of matter parmanus, from which dyads and triads combine to form the material world.

Answer: (A) Indivisible

Explanation:
The Greek word atomos translates to indivisible, reflecting the belief that these particles could not be broken down further.

Answer: (A) He needed to explain how an atom, despite containing negative electrons, remains overall neutral

Explanation:
Since electrons carry negative charge but atoms are neutral overall, Thomson needed a source of positive charge to balance them out — hence the positively charged sphere with embedded electrons.

Answer: (A) Discovery of the electron, gold foil experiment, discovery of the proton, discovery of the neutron

Explanation:
Thomson found the electron in 1897, Geiger and Marsden performed the gold foil experiment in 1911 which led Rutherford to identify the proton soon after, and Chadwick discovered the neutron much later, in 1932.

Answer: (A) The positive charge and most of the mass are packed into an extremely small region

Explanation:
Only a dense, concentrated positive core could repel a fast-moving alpha particle strongly enough to send it back the way it came; a spread-out charge, as Thomson imagined, could never do this.

Answer: (A) Proton

Explanation:
Rutherford identified and named the proton after concluding that the nucleus must carry all the positive charge of the atom.

Answer: (A) It keeps a constant energy without radiating any while circling the nucleus

Explanation:
Bohr's key idea was that within a fixed shell an electron's energy stays constant even though it keeps moving — this is exactly what solved the stability problem that had troubled Rutherford's model.

Answer: (A) Nucleons

Explanation:
Protons and neutrons together are referred to as nucleons, and their combined count gives the mass number of an atom.

Answer: (A) Neutrons weaken the mutual repulsion between the growing number of protons and add extra binding force holding the nucleus together

Explanation:
As protons increase, so does the repulsive force between them since they all carry the same charge. Extra neutrons create distance between protons and reinforce the nuclear force, keeping the heavier nucleus from flying apart.

Answer: (A) Ernest Rutherford

Explanation:
Chadwick worked under Rutherford at the Cavendish Laboratory when he identified the neutron in 1932, finally explaining why atomic masses were higher than what protons alone could account for.

Answer: (A) Co

Explanation:
The chapter notes that cobalt should be written as Co, not CO, since only the first letter of a symbol is capitalised while any following letter stays lowercase.

Answer: (A) 16

Explanation:
Mass number equals protons plus neutrons, so neutrons = 31 - 15 = 16.

Answer: (A) Valence electrons

Explanation:
These outer-shell electrons decide how many electrons an atom can lose, gain or share, which is why they directly determine its valency.

Answer: (A) Isobars

Explanation:
• Different elements, so atomic numbers differ (20, 19, 18)
• Same total number of nucleons, so mass number is identical for all three
• Atoms sharing an identical mass number but differing atomic numbers are termed isobars

Answer: (A) It factors in how commonly each isotope actually occurs in nature

Explanation:
A plain average treats both isotopes as equally common, but chlorine-35 actually makes up about three-quarters of natural chlorine while chlorine-37 makes up the rest; multiplying each mass by its real abundance before adding gives a figure, 35.5 u, that truly reflects how chlorine exists in nature.

Answer: (A) It was grounded in scientific experiments rather than pure imagination

Explanation:
Kanada's parmanus and the Greek atomos were imaginative ideas with no experimental backing. Dalton's theory, proposed in 1808, was the first description of atomic structure supported by actual experimental evidence of that era.

Answer: (A) Electrons must be a basic component present in atoms of every element

Explanation:
Since the rays did not depend on the cathode material or the gas, they could not be something unique to one substance. This pointed to electrons being a universal building block found inside atoms of all elements.

Answer: (B) Most of the volume of an atom is empty space

Explanation:
If the atom's interior were densely packed, far more particles would have been deflected. Since nearly all of them passed straight through, Rutherford reasoned that atoms are largely hollow, with only a tiny region carrying mass and charge.

Answer: (B) Barkla, who first identified X-ray lines, left earlier letters free in case an undiscovered series existed

Explanation:
Physicist Charles Barkla named the first X-ray line he observed as the K line, deliberately skipping A through J to leave space for any earlier series that might later be found, though none ever was. Bohr simply carried this same labelling scheme over to atomic shells.

Answer: (C) Chadwick's discovery of the neutron

Explanation:
The extra, unexplained mass came from a particle in the nucleus that had weight but no charge. Chadwick identified this particle in 1932 and named it the neutron, showing that nuclear mass comes from protons and neutrons together.

Answer: (B) With exactly four valence electrons, losing or gaining electrons is not an easier path to a stable octet, so sharing works better

Explanation:
Elements with fewer than four valence electrons tend to lose them, and those with more than four tend to gain them, to complete an octet. Sitting right in the middle, carbon achieves stability by sharing four electrons with other atoms instead, giving it a valency of four.

Answer: (C) They have the same number of electrons and hence the same electronic configuration

Explanation:
Chemical behaviour is governed mainly by the arrangement of valence electrons. Since isotopes of an element share the same atomic number, and therefore the same number of electrons, their chemical properties stay alike even though their physical properties, such as boiling point, can differ.

Answer: (B) The Latin names of the elements

Explanation:
Berzelius suggested deriving symbols from elements' Latin names, replacing Dalton's earlier pictorial symbols. This is why, for instance, iron carries the symbol Fe, taken from the Latin word ferrum.

Answer: (C) The mass number

Explanation:
• The mass number (A) is written as a superscript on the upper left of the element's symbol.
• The atomic number (Z) is written below it, as a subscript.
• For carbon, this notation appears as 12 over 6, showing a mass number of 12 and an atomic number of 6.

Answer: (A) A revolving electron keeps changing direction, so it accelerates and radiates energy, causing it to spiral into the nucleus

Explanation:
A charged particle moving in a circle is always changing direction, which counts as acceleration; classically, an accelerating charge must radiate energy. Applied to an orbiting electron, this meant it should continuously lose energy and spiral inward until crashing into the nucleus, which would make atoms collapse - something that clearly does not happen in reality.