Chemistry

Total Questions: 69

1. According to Dalton's Atomic Theory, the smallest indivisible particles of matter are called. [S.S.C. Online CHSL (T-I) 7.03.2018 (Shift-II)]

(a) Molecule
(b) Atom
(c) Compound
(d) Element

Correct Answer: (b) Atom

Solution:John Dalton's atomic theory, proposed in the early 19th century, stated that all matter is made up of extremely small particles called atoms, which are indivisible and indestructible. While we now know that atoms are indeed divisible into subatomic particles (protons, neutrons, and electrons), Dalton's theory was a foundational concept in the development of modern chemistry.

2. Who among the following is considered the 'Father of Modern Atomic Theory'? [S.S.C. Online C.H.S.L. (T-I) 4.08.2021 (Shift-I)]

(a) John Dalton
(b) Otto Hahn
(c) Robert Boyle
(d) Willard Gibbs

Correct Answer: (a) John Dalton

Solution:John Dalton, an English chemist and physicist, formulated his atomic theory around the early 1800s. This theory proposed fundamental ideas about the nature of matter, including that all matter is made of atoms, atoms of a given element are identical, and chemical reactions involve the rearrangement of atoms. While some aspects of his original theory have been modified over time with further discoveries, Dalton's work laid the essential groundwork for our modern understanding of atoms and molecules.

3. Who observed that in a mixture of non-reactive gases, the total gas pressure is equal to the sum of the partial pressures of the individual gases? [S.S.C. One CHSL (T-I) 02.06.2022 (Shift-II)]

(a) Antoine Lavoisier
(b) John Dalton
(c) Robert Boyle
(d) Amedeo Avogadro

Correct Answer: (b) John Dalton

Solution:This principle is known as Dalton's Law of Partial Pressures, which he formulated in the early 19th century. This law states that the total pressure exerted by a mixture of non-reacting gases is equal to the sum of the partial pressures of the individual gases.The partial pressure of a gas in a mixture is the pressure that the gas would exert if it occupied the same volume alone at the same temperature.

4. The atomic number of an element is determined by- [S.S.C. Online MTS (T-I) 21.09.2017]

(a) the sum of the number of electrons and protons in an atom
(b) the number of neutrons in the atom
(c) Valency of the element
(d) the number of protons in the atom

Correct Answer: (d) the number of protons in the atom

Solution:

The atomic number (often denoted by the symbol Z) is a fundamental property of a chemical element. It uniquely identifies the element and determines its place in the periodic table. The number of protons in the nucleus of an atom defines which element it is. For example, all atoms with 6 protons are carbon atoms.

While a neutral atom has an equal number of protons and electrons, the atomic number is specifically based on the count of protons, as this number remains constant for all isotopes of a particular element, whereas the number of neutrons can vary (leading to isotopes), and the number of electrons can change (leading to ions).

5. An atom is- [S.S.C. Online MTS (T-I) 16.09.2017]

(a) the smallest known particle of matter.
(a) the smallest known particle of matter.
(c) the smallest indivisible particle of an element, which can take part in a chemical change.
(d) a charged particle.

Correct Answer: (c) the smallest indivisible particle of an element, which can take part in a chemical change.

Solution:An atom is the smallest indivisible particle of matter, which can take part in a chemical change or chemical reaction, i.e. It is the smallest particle representing matter in a chemical reaction.

6. Sub-atomic particles of atoms are- [S.S.C. Online MTS (T-1) 6.10.2017]

(a) Only protons
(b) Only neutron
(c) Both protons & neutron
(d) Proton, electron & neutron

Correct Answer: (d) Proton, electron & neutron

Solution:

Atoms are composed of three main subatomic particles:

Protons: Positively charged particles located in the nucleus (the atom's central core).
Neutrons: Neutrally charged particles (no electric charge) also located in the nucleus.
Electrons: Negatively charged particles that orbit the nucleus in specific energy levels or shells.

7. All isotopes of the same element have: [S.S.C. Online Graduate Level (T-I) 31.08.201]

(a) different atomic numbers and different atomic mass.
(b) different atomic numbers and the same atomic mass.
(c) the same atomic number but different atomic masses.
(d) the same atomic number and the same atomic mass.

Correct Answer: (c) the same atomic number but different atomic masses.

Solution:
Atomic Number:
The atomic number of an element is defined by the number of protons in the nucleus of its atoms. All isotopes of the same element have the same number of protons, hence the same atomic number. This is what defines the element.

Atomic Mass:
The atomic mass is approximately the sum of the number of protons and neutrons in the nucleus. Isotopes of the same element have the same number of protons but differ in the number of neutrons. This difference in the number of neutrons leads to different atomic masses for the isotopes of that element.

For example, Carbon-12, Carbon-13, and Carbon-14 are all isotopes of carbon. They all have an atomic number of 6 (6 protons), but they have 6, 7, and 8 neutrons respectively, resulting in different atomic masses.

8. Atoms of the same element having different mass numbers are called- [S.S.C. Online Graduate Level (T-I) 2.09.2016]

(a) Isobars
(b) Isotopes
(c) Isotones
(d) Isomers

Correct Answer: (b) Isotopes

Solution:Atoms of the same element, which have the same atomic number but different atomic mass or mass numbers, are called isotopes. An isotope atom has the same number of protons and a different number of neutrons. Atoms of different elements having different atomic numbers but the same mass number are called isobars.

9. Isotopes of an element have- [S.S.C. Online CL (T-I) 22.03.2018]

(a) Same physical propertie
(b) Different chemical properties
(c) Different number of neutrons
(d) Different atomic number

Correct Answer: (c) Different number of neutrons

Solution:
Isotopes are atoms of the same element that have the same number of protons (which defines the element and its atomic number) but a different number of neutrons.

10. Isobars have_________. [S.S.C. Online CHSL (T-I) 11.01.2017]

(a) Same mass numbers but different atomic numbers.
(b) Different mass numbers but same atomic numbers.
(c) Same mass and atomic numbers.
(d) Different mass and atomic numbers.

Correct Answer: (a) Same mass numbers but different atomic numbers.

Solution:Isobars are atoms of different chemical elements that have the same number of nucleons (protons + neutrons), which means they have the same mass number.

However, because they are different elements, they must have a different number of protons, and therefore a different atomic number.

For example, Argon-40 (atomic number 18) and Calcium-40 (atomic number 20) are isobars. They both have a mass number of 40, but they are different elements due to their different numbers of protons.

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