Atomic Structure — Set 4
Chemistry · परमाणु संरचना · Questions 31–40 of 50
Which subatomic particle is not found in the nucleus of a typical atom?
Correct Answer: A. Electron
Electrons are located outside the nucleus in specific regions called orbitals or shells. The nucleus is reserved for protons and neutrons, collectively known as nucleons. This separation defines the physical volume of the atom.
What determines the chemical properties of an element?
Correct Answer: C. Number of valence electrons
Valence electrons are the ones involved in forming chemical bonds with other atoms. Elements with the same number of valence electrons show similar chemical reactions. This is the basis for the vertical groups in the periodic table.
Which scientist developed the 'Plum Pudding' model of the atom?
Correct Answer: B. J.J. Thomson
J.J. Thomson envisioned the atom as a sphere of positive charge with electrons embedded in it. This was the first model to include subatomic particles. It was later disproved by the gold foil experiment.
What is the maximum number of electrons that can be held in the first energy level (n=1)?
Correct Answer: A. 2
The first energy level consists of only one 's' orbital. According to the $2n^2$ rule, it can hold at most 2 electrons. This explains why the first row of the periodic table has only two elements.
Which of the following is true for neutral atoms of the same element?
Correct Answer: D. They have the same number of protons
All atoms of a specific element must have the same number of protons. If the proton count changes, the atom becomes a different element. This number is the defining characteristic of the element's identity.
The mass number of an atom is defined as the sum of?
Correct Answer: D. Protons and neutrons
The correct answer is 'Protons and neutrons'. Mass number counts the total number of particles inside the nucleus. Since electrons have negligible mass, they are not included in this sum. It is always represented as a whole number.
Who proposed that electrons move in discrete orbits with fixed energy?
Correct Answer: A. Niels Bohr
Niels Bohr introduced the concept of quantized energy levels for electrons. He argued that electrons do not lose energy while moving in these specific paths. This solved the problem of why atoms are stable.
What kind of charge does the nucleus of an atom carry?
Correct Answer: D. Positive
The nucleus contains protons, which are positive, and neutrons, which have no charge. Consequently, the overall charge of the nucleus is always positive. The magnitude depends on the number of protons present.
Which subatomic particle's mass is approximately equal to that of a proton?
Correct Answer: D. Neutron
Protons and neutrons are very similar in mass, both being around 1 atomic mass unit. The neutron is slightly heavier than the proton. This similarity is why they are both considered nucleons.
An atom of an element has 11 protons and 12 neutrons. What is its mass number?
Correct Answer: A. 23
Mass number is calculated by adding the number of protons and neutrons together. Here, $11 + 12 = 23$, which identifies the atom as an isotope of Sodium. The number of electrons would also be 11 if the atom is neutral.