Electronic Configuration — Homi Bhabha Class 9 Chemistry MCQs with Solutions
Free Homi Bhabha Class 9 Chemistry Electronic Configuration MCQs with step-by-step solutions (12 questions). Part of Periodic Classification & Chemical Bonding. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Electronic Configuration · medium · numerical
The maximum number of electrons that the first shell (K) of an atom can hold is:
A. 2 ✓ Correct
B. 1
C. 8
D. 18
Solution: By the $2n^2$ rule, the K shell ($n=1$) holds $2 \times 1^2 = 2$ electrons.
Q2 — Electronic Configuration · medium · numerical
The maximum number of electrons in the second shell (L) is:
A. 32
B. 8 ✓ Correct
C. 2
D. 18
Solution: For $n=2$, maximum $= 2 \times 2^2 = 8$ electrons.
Q3 — Electronic Configuration · hard · theory
The electronic configuration of a sodium atom (atomic number 11) is:
A. 2, 9
B. 2, 8, 1 ✓ Correct
C. 2, 8, 8
D. 8, 2, 1
Solution: Filling shells: 2 in K, 8 in L, 1 in M gives 2, 8, 1.
Q4 — Electronic Configuration · medium · theory
The electrons present in the outermost shell of an atom are called:
A. core electrons
B. nucleons
C. valence electrons ✓ Correct
D. free electrons
Solution: Outer-shell electrons are valence electrons and decide chemical behaviour.
Q5 — Electronic Configuration · hard · numerical
The number of valence electrons in a chlorine atom (configuration 2, 8, 7) is:
A. 8
B. 2
C. 17
D. 7 ✓ Correct
Solution: The outermost shell has 7 electrons, so chlorine has 7 valence electrons.
Q6 — Electronic Configuration · hard · theory
An atom is chemically stable when its outermost shell contains ______ electrons (octet), except for the first shell which needs 2:
A. 4
B. 18
C. 2
D. 8 ✓ Correct
Solution: A complete octet (8 electrons) in the outer shell gives special stability (duplet for the first shell).
Q7 — Electronic Configuration · medium · theory
An element with the electronic configuration 2, 8, 8 is:
A. hydrogen
B. a noble gas (argon) ✓ Correct
C. a reactive metal
D. a halogen
Solution: The complete outer octet (2, 8, 8) is that of the noble gas argon (atomic number 18).
Q8 — Electronic Configuration · easy · theory
According to the 2n squared rule, the maximum number of electrons that the second shell (L shell) can hold is
A. 2
B. 18
C. 8 ✓ Correct
D. 32
Solution: The maximum number of electrons in a shell is 2n². For the L shell n = 2, so 2 × (2)² = 8 electrons.
Q9 — Electronic Configuration · medium · theory
An atom has the electronic configuration 2, 8, 7. To which group and period of the periodic table does it belong?
A. Group 17, Period 3 ✓ Correct
B. Group 2, Period 8
C. Group 7, Period 2
D. Group 8, Period 7
Solution: The number of occupied shells (3) gives the period (3), and the 7 valence electrons place it in Group 17, the halogens. This element is chlorine.
Q10 — Electronic Configuration · medium · numerical
An atom of an element contains 19 electrons. What is its correct electronic configuration?
A. 2, 8, 8, 1 ✓ Correct
B. 2, 9, 8
C. 2, 8, 9
D. 2, 8, 7, 2
Solution: Filling the shells in order 2, then 8, then 8 uses 18 electrons; the remaining single electron goes into the fourth shell, giving 2, 8, 8, 1 (potassium). A shell cannot hold 9 electrons at this stage.
Q11 — Electronic Configuration · hard · theory
The atom of an element has 2 electrons in its K shell and 8 electrons in its L shell, with no other electrons. Which statement about this element is correct?
A. It is a metal with valency 8
B. It is a noble gas that is chemically inert with valency 0 ✓ Correct
C. It is a halogen that gains one electron
D. It is a reactive metal with valency 2
Solution: The configuration 2, 8 (10 electrons, neon) has a completely filled outermost shell. Such an atom has no tendency to gain, lose or share electrons, so it is a chemically inert noble gas with valency 0.
Q12 — Electronic Configuration · hard · theory
Two atoms P and Q have the electronic configurations 2, 8, 2 and 2, 8, 8, 2 respectively. Which conclusion is correct?
A. P and Q have completely different valencies
B. Both belong to Group 2 and show similar chemical properties ✓ Correct
C. Q is a non-metal
D. Both belong to the same period
Solution: Both atoms have 2 valence electrons, so both lie in Group 2 and behave similarly (like magnesium and calcium). Q simply has one extra shell, so it is a larger atom placed in a lower period.