Attempt each question, then reveal the answer to check yourself.
Question 1 — Atomic Structure
The number of neutrons in an atom of sodium with mass number 23 and atomic number 11 is
A. 34
B. 12
C. 11
D. 23
Answer: B. Neutrons = mass number − atomic number = 23 − 11 = 12.
Question 2 — Isotopes
Isotopes of an element have the same number of
A. Protons
B. Neutrons
C. Electrons and neutrons
D. Protons and neutrons
Answer: A. Isotopes have the same atomic number (protons) but different mass numbers (neutrons).
Question 3 — Bonding
An ionic bond is formed by the
A. Sharing of electrons
B. Transfer of electrons
C. Sharing of protons
D. Transfer of protons
Answer: B. Ionic bonds involve electron transfer (metal loses, non-metal gains); covalent bonds involve sharing.
Question 4 — Acids
Which of the following turns blue litmus paper red?
A. Sodium hydroxide solution
B. Dilute hydrochloric acid
C. Distilled water
D. Ammonia solution
Answer: B. Acids turn blue litmus red. The others are alkaline (A, D) or neutral (C).
Question 5 — Mole Concept
How many moles are there in 4 g of NaOH? (Na = 23, O = 16, H = 1)
A. 4.0 mol
B. 0.4 mol
C. 0.1 mol
D. 40 mol
Answer: C. Mᵣ of NaOH = 40. Moles = 4 ÷ 40 = 0.1 mol.
Question 6 — Theory
State three differences between ionic and covalent compounds.
Model answer (any three):
1. Ionic compounds have high melting points; covalent compounds have low melting points. 2. Ionic compounds conduct electricity when molten or dissolved; covalent compounds generally do not. 3. Ionic bonds involve electron transfer; covalent bonds involve electron sharing. 4. Ionic compounds are usually solids; covalent compounds are often liquids or gases.
Question 7 — Theory
Write the electronic configuration of calcium (atomic number 20) and state the formula of its ion.
Answer: Electronic configuration = 2, 8, 8, 2. Calcium loses 2 electrons to form the ion Ca²⁺.
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