Chemical Reactivity — Homi Bhabha Class 9 Chemistry MCQs with Solutions
Free Homi Bhabha Class 9 Chemistry Chemical Reactivity 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 — Chemical Reactivity · medium · theory
Noble gases are chemically unreactive because their outermost shells are:
A. empty
B. completely filled (stable octet/duplet) ✓ Correct
C. always losing electrons
D. half filled
Solution: A complete outer shell makes noble gases stable, so they rarely react.
Q2 — Chemical Reactivity · hard · theory
An atom with only 1 electron in its outermost shell is:
A. a noble gas
B. a reactive metal that easily loses that electron ✓ Correct
C. chemically inert
D. a reactive non-metal that gains electrons
Solution: Losing the single valence electron gives a stable octet, so such atoms are reactive metals (e.g. Na).
Q3 — Chemical Reactivity · hard · theory
An atom with 7 electrons in its outermost shell tends to:
A. lose 7 electrons
B. gain 1 electron and act as a reactive non-metal ✓ Correct
C. lose 1 electron
D. stay inert
Solution: Gaining one electron completes the octet, so such atoms are reactive non-metals (e.g. Cl).
Q4 — Chemical Reactivity · medium · theory
The chemical reactivity of an element is mainly decided by the number of:
A. protons in the nucleus
B. neutrons
C. shells only
D. valence electrons ✓ Correct
Solution: Valence (outer-shell) electrons determine how an atom bonds and reacts.
Q5 — Chemical Reactivity · hard · theory
As we move down Group 1 (alkali metals), the chemical reactivity:
A. becomes zero
B. increases ✓ Correct
C. remains the same
D. decreases
Solution: Down the group the valence electron is farther from the nucleus and lost more easily, so reactivity increases.
Q6 — Chemical Reactivity · medium · theory
When a metal reacts, it usually ______ electrons, and when a non-metal reacts, it usually ______ electrons:
A. gains; loses
B. shares; loses
C. loses; shares
D. loses; gains ✓ Correct
Solution: Metals tend to lose valence electrons (forming cations); non-metals tend to gain them (forming anions).
Q7 — Chemical Reactivity · hard · theory
Atoms take part in chemical reactions mainly to achieve:
A. radioactivity
B. a stable noble-gas electronic configuration ✓ Correct
C. more neutrons
D. a higher atomic mass
Solution: Atoms react to complete their outer shell and reach the stable configuration of the nearest noble gas.
Q8 — Chemical Reactivity · easy · theory
Which of the following families of elements is the LEAST reactive?
A. Halogens
B. Alkaline earth metals
C. Noble gases ✓ Correct
D. Alkali metals
Solution: Noble gases (Group 18) have completely filled outermost shells, so they have almost no tendency to gain, lose or share electrons, which makes them the least reactive family.
Q9 — Chemical Reactivity · easy · theory
Metals become chemically reactive mainly by
A. keeping all their electrons unchanged
B. losing their valence electrons to form positive ions ✓ Correct
C. gaining electrons to form negative ions
D. sharing electrons equally with other metals
Solution: Metals have only a few loosely held valence electrons. They react by losing these electrons to form positive ions, which is why elements such as sodium and potassium are very reactive.
Q10 — Chemical Reactivity · medium · theory
As we move down Group 1 from lithium to sodium to potassium, the reactivity of the metals
A. increases because the outer electron is farther from the nucleus and is lost more easily ✓ Correct
B. decreases because the number of valence electrons falls
C. remains exactly the same throughout the group
D. decreases because the atoms become smaller
Solution: Going down the group the atom becomes larger and its single valence electron is held less tightly by the nucleus, so it is lost more easily. Easier loss of the electron means greater reactivity.
Q11 — Chemical Reactivity · hard · theory
Fluorine is more reactive than chlorine, even though both are halogens that react by gaining one electron. The best reason is that
A. the fluorine atom is smaller, so its nucleus attracts an incoming electron more strongly ✓ Correct
B. fluorine loses electrons more readily than chlorine
C. fluorine has more electron shells than chlorine
D. fluorine is a metal while chlorine is a non-metal
Solution: Non-metals react by gaining electrons. The smaller fluorine atom holds an added electron closer to its nucleus, so it attracts an extra electron more strongly than the larger chlorine atom, making fluorine more reactive.
Q12 — Chemical Reactivity · hard · theory
Assertion: Noble gases normally do not take part in chemical reactions. Reason: The outermost shells of noble gas atoms are completely filled with electrons. Choose the correct option.
A. Both assertion and reason are true and the reason correctly explains the assertion ✓ Correct
B. The assertion is false but the reason is true
C. The assertion is true but the reason is false
D. Both assertion and reason are true but the reason does not explain the assertion
Solution: A completely filled outermost shell is a very stable arrangement, so noble gas atoms have no tendency to gain, lose or share electrons. The reason is therefore the correct explanation of why noble gases are unreactive.