Isotopes — Homi Bhabha Class 9 Chemistry MCQs with Solutions
Free Homi Bhabha Class 9 Chemistry Isotopes MCQs with step-by-step solutions (8 questions). Part of Atoms, Molecules & Structure. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Isotopes · medium · theory
Isotopes of an element have the same number of ______ but a different number of ______:
A. electrons; protons
B. neutrons; protons
C. protons; neutrons ✓ Correct
D. protons; electrons
Solution: Isotopes have the same atomic number (protons) but different mass numbers (neutrons).
Q2 — Isotopes · medium · theory
Carbon-12 and Carbon-14 are isotopes because they have the same number of protons but different numbers of:
A. electrons
B. protons
C. molecules
D. neutrons ✓ Correct
Solution: Both have 6 protons; C-12 has 6 neutrons and C-14 has 8 neutrons.
Q3 — Isotopes · hard · theory
Isotopes of an element show ______ chemical properties because they have the same ______:
A. identical; number of electrons (electronic configuration) ✓ Correct
B. different; number of neutrons
C. identical; number of neutrons
D. different; atomic number
Solution: Chemical behaviour depends on electrons; isotopes have the same electron arrangement, so identical chemistry.
Q4 — Isotopes · hard · numerical
Two isotopes of an element have mass numbers 35 and 37 with atomic number 17. The numbers of neutrons in them are:
A. 18 and 20 ✓ Correct
B. 18 and 18
C. 35 and 37
D. 17 and 17
Solution: Neutrons $= A - Z$: $35 - 17 = 18$ and $37 - 17 = 20$.
Q5 — Isotopes · medium · theory
The isotope used for carbon dating of ancient fossils is:
A. Carbon-14 ✓ Correct
B. Cobalt-60
C. Carbon-12
D. Uranium-235
Solution: The radioactive isotope Carbon-14 is used to estimate the age of once-living materials.
Q6 — Isotopes · easy · theory
Isotopes are atoms of the same element that have:
A. The same mass number but different atomic numbers
B. Different numbers of both protons and electrons
C. The same number of neutrons but different numbers of protons
D. The same number of protons but different numbers of neutrons ✓ Correct
Solution: Isotopes share the same atomic number (protons) but differ in the number of neutrons, giving them different mass numbers.
Q7 — Isotopes · medium · theory
Chlorine occurs as two isotopes, Cl-35 and Cl-37. Which statement about them is correct?
A. They have the same number of protons and electrons but differ in neutrons ✓ Correct
B. They have different chemical properties
C. Cl-37 has two more protons than Cl-35
D. They have different atomic numbers
Solution: Isotopes have identical proton and electron counts (hence identical chemistry) and differ only in the number of neutrons.
Q8 — Isotopes · hard · numerical
Chlorine consists of Cl-35 and Cl-37 with relative abundances of 75% and 25% respectively. Its average atomic mass is closest to:
A. 35.5 u ✓ Correct
B. 36.0 u
C. 37.0 u
D. 35.0 u
Solution: Average atomic mass = (35 x 0.75) + (37 x 0.25) = 26.25 + 9.25 = 35.5 u.