Mass Number MCQs Quiz | Class 9
This Class IX Science (Code 086) quiz covers Unit I: Matter – Its Nature and Behaviour, focusing specifically on Mass Number. The questions explore the definition of mass number, its relation to protons and neutrons, and how it differs from atomic number. Students can attempt these 10 MCQs to test their understanding, check their score instantly, and download a detailed answer key PDF for revision.
Understanding Mass Number
Mass Number is a fundamental concept in nuclear chemistry and physics, representing the total count of nucleons in an atomic nucleus.
Key Concepts
- Definition: The mass number (represented by the symbol A) is defined as the sum of the total number of protons and neutrons present in the nucleus of an atom.
- Nucleons: Protons and neutrons are collectively known as nucleons because they reside in the nucleus.
- Formula: Mass Number (A) = Atomic Number (Z) + Number of Neutrons (n).
- Notation: In the standard notation of an element, the mass number is written as a superscript on the left side of the element symbol (e.g., in Carbon-12, written as 12C, the mass number is 12).
Subatomic Particles and Mass
| Particle | Location | Contribution to Mass Number |
|---|---|---|
| Proton | Nucleus | Yes (1 unit approx) |
| Neutron | Nucleus | Yes (1 unit approx) |
| Electron | Orbitals | No (Negligible mass) |
Relationship with Atomic Number
While the Atomic Number (Z) identifies the element (number of protons), the Mass Number (A) identifies the specific isotope. For example, Carbon-12 and Carbon-14 are isotopes of Carbon; they have the same Z (6) but different A (12 and 14) due to a different number of neutrons.
Quick Revision Points
- Mass number is always a whole number for a specific atom.
- Number of Neutrons = Mass Number (A) – Atomic Number (Z).
- Electrons do not contribute significantly to the mass of an atom.
- Isobars: Atoms of different elements with different atomic numbers but the same mass number (e.g., Calcium-40 and Argon-40).
Extra Practice Questions
- Calculate the number of neutrons in a Sodium atom (Mass Number 23, Atomic Number 11).
- Why is the mass of an atom concentrated in the nucleus?
- Write the standard notation for an atom with 8 protons and 8 neutrons.
- Differentiate between Mass Number and Atomic Mass.
- If an atom has a mass number of 40 and 20 protons, identify the element.
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