Radioactivity Practice Questions
KCSE (Kenya) · KCSE Physics · 140 free MCQs with instant results and detailed explanations.
140
Total
43
Easy
70
Medium
27
Hard
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Sample Questions from Radioactivity
Here are 10 sample questions. Start a quiz to get randomized questions with scoring.
Q1
Easy
Which type of radiation can penetrate the skin but not the bone?
A.
Alpha radiation
B.
Beta radiation
C.
Gamma radiation
D.
X-ray radiation
Show Answer & Explanation
Correct Answer: B
Beta radiation consists of electrons that can penetrate the skin but are generally stopped by denser materials like bone. Therefore, option B is the correct answer.
Q2
Easy
What is the primary type of radiation emitted during alpha decay?
A.
Alpha particles
B.
Beta particles
C.
Gamma rays
D.
Neutrons
Show Answer & Explanation
Correct Answer: A
Alpha decay involves the emission of alpha particles, which are composed of 2 protons and 2 neutrons. This type of radiation is distinctive to alpha decay.
Q3
Easy
Which of the following statements is true regarding beta particles?
A.
They are positively charged.
B.
They have a mass similar to that of protons.
C.
They can penetrate materials more easily than alpha particles.
D.
They are emitted during gamma decay.
Show Answer & Explanation
Correct Answer: C
Beta particles, which are negatively charged electrons or positrons, can penetrate materials more easily than alpha particles because they are much smaller and lighter.
Q4
Medium
If a radioactive substance has a half-life of 5 years, how much of a 40g sample remains after 15 years?
A.
20g
B.
10g
C.
5g
D.
2.5g
Show Answer & Explanation
Correct Answer: B
After 15 years, which is three half-lives (5 years each), the remaining amount of the substance is 40g / 2^3 = 40g / 8 = 5g.
Q5
Medium
What is the result of a beta decay in terms of atomic and mass numbers?
A.
Increases atomic number by 1, mass number unchanged
B.
Decreases atomic number by 1, mass number unchanged
C.
Increases atomic number by 1, mass number increases by 1
D.
Decreases atomic number by 1, mass number decreases by 1
Show Answer & Explanation
Correct Answer: A
In beta decay, a neutron is converted into a proton, which increases the atomic number by 1 while keeping the mass number the same, since a proton is added without losing a neutron.
Q6
Medium
Which of the following is a common application of radioactive isotopes in medicine?
A.
Radiotherapy for cancer treatment
B.
Water purification
C.
Food preservation
D.
Plastic manufacturing
Show Answer & Explanation
Correct Answer: A
Radiotherapy utilizes radioactive isotopes to target and kill cancer cells, making it a well-known application of radioactivity in the medical field.
Q7
Medium
What type of radiation is emitted during alpha decay?
A.
High-energy electrons
B.
Helium nuclei
C.
High-energy photons
D.
Protons
Show Answer & Explanation
Correct Answer: B
Alpha decay involves the emission of alpha particles, which are essentially helium nuclei consisting of 2 protons and 2 neutrons.
Q8
Hard
A radioactive substance has a half-life of 5 years. If you start with 80 grams of the substance, how much will remain after 15 years?
A.
10 grams
B.
20 grams
C.
5 grams
D.
40 grams
Show Answer & Explanation
Correct Answer: A
After 15 years (which is 3 half-lives), the amount of substance remaining is calculated as follows: 80 g -> 40 g (after 5 years) -> 20 g (after 10 years) -> 10 g (after 15 years). Thus, 10 grams remain.
Q9
Hard
A certain isotope emits beta particles and has a decay constant of 0.693 per year. What is the half-life of this isotope?
A.
1 year
B.
0.693 years
C.
2 years
D.
0.5 years
Show Answer & Explanation
Correct Answer: A
The half-life (T1/2) can be calculated using the formula T1/2 = ln(2) / decay constant. Here, ln(2) is approximately 0.693. Therefore, T1/2 = 0.693 / 0.693 = 1 year.
Q10
Hard
A sample of a radioactive substance has a half-life of 5 years. If you start with 80 grams of the substance, how much will remain after 15 years?
A.
10 grams
B.
20 grams
C.
40 grams
D.
5 grams
Show Answer & Explanation
Correct Answer: A
After 15 years, which is three half-lives (5 years each), the amount remaining is 80 grams divided by 2 three times: 80 -> 40 -> 20 -> 10 grams.
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Radioactivity — KCSE (Kenya) KCSE Physics Practice Questions Online
This page contains 140 practice MCQs for the chapter Radioactivity in KCSE (Kenya) KCSE Physics. The questions are organized by difficulty — 43 easy, 70 medium, 27 hard — so you can choose the right level for your preparation.
Every question includes a detailed explanation to help you understand the concept, not just memorize answers. Take a timed quiz to simulate exam conditions, or practice at your own pace with no time limit.