Q1
The nucleus of an atom contains:
Aprotons and neutrons
Bonly electrons
Conly protons
Donly neutrons
CBSEClass 9 (CBSE)ScienceCh 4 · Topic 1
Sub-atomic Particles
Learning about the particles that make up an atom - protons, neutrons and electrons.
Core concept
The number of protons in an atom's nucleus, called the atomic number, uniquely identifies each element — for example, all atoms with exactly 6 protons are carbon atoms, regardless of how many neutrons they have. Atoms of the same element with different numbers of neutrons are called isotopes — for instance, carbon-12 and carbon-14 are both carbon but have different neutron counts, giving them slightly different masses while retaining identical chemical properties.
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• Protons: positive charge, in nucleus. Neutrons: neutral charge, in nucleus. Electrons: negative charge, orbiting nucleus.
• Protons and neutrons contribute nearly all of an atom's mass.
• Atomic number = number of protons, uniquely identifying an element.
• Isotopes are atoms of the same element with different numbers of neutrons.