Atomic Structure — Set 1
Chemistry · परमाणु संरचना · Questions 1–10 of 50
Which subatomic particle was discovered by J.J. Thomson using the cathode ray tube experiment?
Correct Answer: A. Electron
The electron was identified by J.J. Thomson through his work with cathode rays. This discovery proved that atoms contain negatively charged particles. He later proposed the 'Plum Pudding' model to describe atomic structure.
What is the primary reason an atom is electrically neutral under normal conditions?
Correct Answer: D. Equal number of protons and electrons
The positive charge of protons is exactly balanced by the negative charge of electrons. In a neutral atom, these two types of particles must be present in equal numbers. This balance ensures the net charge of the entire atom remains zero.
Which component of the atom contains almost all of its mass but occupies very little space?
Correct Answer: B. Nucleus
The nucleus houses the protons and neutrons which contribute nearly all atomic mass. It is located at the center and is extremely dense compared to the rest of the atom. Rutherford's gold foil experiment was instrumental in identifying this central core.
What name is given to atoms of the same element that have different numbers of neutrons?
Correct Answer: C. Isotopes
Isotopes are variants of a chemical element which differ in neutron count. They possess the same atomic number but different mass numbers. Most elements found in nature exist as a mixture of various isotopes.
Which quantum number determines the primary energy level or shell of an electron?
Correct Answer: C. Principal quantum number
The principal quantum number (n) defines the main energy level of an electron. It relates to the average distance of the electron from the nucleus. Higher values of 'n' indicate shells that are further away from the center.
What is the maximum number of electrons that can be accommodated in the 'M' shell?
Correct Answer: C. 18
The maximum capacity of an electron shell is calculated using the formula $2n^2$. For the M shell, the value of n is 3, resulting in 18 electrons. This rule helps determine the electronic configuration of heavier elements.
Who is credited with the discovery of the neutron in 1932?
Correct Answer: D. James Chadwick
James Chadwick discovered the neutron by bombarding beryllium with alpha particles. This particle carries no electrical charge but has a mass similar to a proton. Its discovery completed the basic model of the atomic nucleus.
Which of the following describes 'Isobars' in chemistry?
Correct Answer: D. Same mass number, different atomic number
Isobars are atoms of different chemical elements that have the same mass number. Because they have different atomic numbers, they occupy different positions in the periodic table. Examples include Calcium-40 and Argon-40.
The 'Uncertainty Principle', which states it is impossible to know both position and momentum exactly, was proposed by?
Correct Answer: D. Werner Heisenberg
Werner Heisenberg formulated this principle as a fundamental limit in quantum mechanics. It suggests that the act of measuring one variable changes the other. This concept shifted atomic theory from fixed orbits to probability clouds.
What is the charge of an Alpha (α) particle?
Correct Answer: A. +2
An alpha particle consists of two protons and two neutrons, making it a helium nucleus. Since it lacks electrons, it carries a net positive charge of +2. These particles are commonly emitted during certain types of radioactive decay.