Atomic Number & Mass Number — Homi Bhabha Class 9 Chemistry MCQs with Solutions
Free Homi Bhabha Class 9 Chemistry Atomic Number & Mass Number 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 — Atomic Number & Mass Number · medium · theory
The atomic number of an element is equal to the number of ______ in its atom:
A. protons ✓ Correct
B. electrons and neutrons
C. neutrons
D. nucleons
Solution: Atomic number (Z) = number of protons in the nucleus (equal to electrons in a neutral atom).
Q2 — Atomic Number & Mass Number · medium · theory
The mass number of an atom is the total number of:
A. protons only
B. protons and neutrons ✓ Correct
C. protons and electrons
D. neutrons and electrons
Solution: Mass number (A) = number of protons + number of neutrons (the nucleons).
Q3 — Atomic Number & Mass Number · hard · numerical
An atom of sodium has atomic number 11 and mass number 23. The number of neutrons in it is:
A. 12 ✓ Correct
B. 11
C. 34
D. 23
Solution: Neutrons $= A - Z = 23 - 11 = 12$.
Q4 — Atomic Number & Mass Number · hard · numerical
An atom has 17 protons and 18 neutrons. Its mass number is:
A. 35 ✓ Correct
B. 17
C. 18
D. 1
Solution: Mass number $= 17 + 18 = 35$ (this is chlorine).
Q5 — Atomic Number & Mass Number · medium · theory
The identity of an element is decided by its:
A. mass number
B. valency
C. atomic number ✓ Correct
D. number of neutrons
Solution: The number of protons (atomic number) uniquely determines which element an atom is.
Q6 — Atomic Number & Mass Number · easy · theory
The atomic number of an element is equal to the number of:
A. Electrons plus neutrons
B. Protons plus neutrons
C. Protons in the nucleus ✓ Correct
D. Neutrons in the nucleus
Solution: The atomic number (Z) is defined as the number of protons in the nucleus of an atom.
Q7 — Atomic Number & Mass Number · medium · numerical
A sodium atom has a mass number of 23 and an atomic number of 11. How many neutrons are present in its nucleus?
A. 12 ✓ Correct
B. 11
C. 23
D. 34
Solution: Number of neutrons = mass number - atomic number = 23 - 11 = 12.
Q8 — Atomic Number & Mass Number · hard · numerical
An ion contains 17 protons, 18 neutrons and 18 electrons. What are its mass number and charge, respectively?
A. 35 and +1
B. 35 and -1 ✓ Correct
C. 53 and -1
D. 18 and -1
Solution: Mass number = protons + neutrons = 17 + 18 = 35. Charge = protons - electrons = 17 - 18 = -1, so it is a -1 ion.