Construction – Practice Questions and
Answers (2025/26 Edition)
1. The rate of decay of a radioactive isotope is measured by its:
a) Half-life
b) Atomic number
c) Mass number
d) pH
Answer: a) Half-life
Rationale: Half-life is the time required for half of a radioactive substance to
decay.
2. Which pH number indicates the greatest acidity?
a) 7
b) 14
c) 1
d) 10
Answer: c) 1
Rationale: pH scale 0–14; lower numbers are more acidic. pH 1 is highly acidic.
3. The approximate mass of a 49 N weight is:
a) 0.5 kg
b) 5 kg
c) 49 kg
d) 9.8 kg
Answer: b) 5 kg
Rationale: Weight = mass × gravity (9.8 m/s²). 49 N ÷ 9.8 ≈ 5 kg.
4. The atomic number of an element is the number of:
a) Neutrons in the nucleus
b) Protons in the nucleus
,c) Electrons in the outer shell
d) Protons plus neutrons
Answer: b) Protons in the nucleus
Rationale: Atomic number = number of protons.
5. Fluorine has an atomic weight of 19 and an atomic number of 9. How many
neutrons are in its nucleus?
a) 9
b) 10
c) 19
d) 28
Answer: b) 10
Rationale: Neutrons = atomic weight – atomic number = 19 – 9 = 10.
6. An atom has 30 protons and 35 neutrons. Its atomic weight is:
a) 30
b) 35
c) 65
d) 95
Answer: c) 65
Rationale: Atomic weight = protons + neutrons = 30 + 35 = 65.
7. Which subatomic particle determines the element’s identity?
a) Neutron
b) Electron
c) Proton
d) Positron
Answer: c) Proton
Rationale: Number of protons defines the element.
8. A pH of 12 indicates:
a) Strong acid
b) Strong base
c) Neutral
d) Slightly acidic
Answer: b) Strong base
Rationale: pH > 7 = basic/alkaline; 12 is strongly basic.
, 9. If an object weighs 98 N on Earth, its mass is approximately:
a) 10 kg
b) 1 kg
c) 98 kg
d) 9.8 kg
Answer: a) 10 kg
Rationale: 98 N ÷ 9.8 m/s² = 10 kg.
10. The atomic weight of an atom is the sum of:
a) Protons and electrons
b) Protons and neutrons
c) Neutrons and electrons
d) Protons only
Answer: b) Protons and neutrons
Rationale: Atomic weight ≈ protons + neutrons.
11. Which pH value is neutral?
a) 0
b) 7
c) 14
d) 10
Answer: b) 7
Rationale: Neutral pH = 7 (pure water).
12. An atom with 8 protons, 8 neutrons, and 8 electrons has atomic weight:
a) 8
b) 16
c) 24
d) 32
Answer: b) 16
Rationale: 8 protons + 8 neutrons = 16.
13. The half-life of a material is 10 years. After 20 years, what fraction remains?
a) 1/2
b) 1/4
c) 1/8
d) 1/16