Q: What are isobars?
A: Isobars are atoms of different elements with different atomic numbers but the same mass number.
Q: Who discovered the neutron?
A: J. Chadwick discovered the neutron in 1932.
Q: Why are noble gases chemically inert?
A: Noble gases have completely filled outermost shells (8 electrons), making them highly stable and unreactive.
Q: How is the average atomic mass of an element calculated?
A: By considering the percentage of each isotope and calculating the weighted average of their masses.
Q: What are some practical applications of isotopes?
A: (i) Uranium isotope used as fuel in nuclear reactors
(ii) Cobalt isotope used in cancer treatment
(iii) Iodine isotope used in treating goitre
Q: What was a major limitation of Rutherford’s atomic model?
A: The model could not explain why electrons do not lose energy and fall into the nucleus, which would make atoms unstable.
Q: How do atoms achieve stability?
A: By gaining, losing, or sharing electrons to achieve a full octet (8 electrons) in the outermost shell.
Q: How is an atom’s electronic configuration represented?
A: By writing the number of electrons in each shell, starting from the innermost shell (K), such as 2,8,1 for sodium.
Q: How does the number of electrons relate to the atom’s charge?
A: When the number of electrons equals the number of protons, the atom is neutral. If electrons are gained or lost, the atom becomes an ion with a negative or positive charge.
Class 9 Science The Fundamentals of Life Extra Question Answer
