Which of the following best describes the Bohr model of the atom?

A. Electrons move in fixed orbits around the nucleus.

B. Electrons move randomly within a cloud around the nucleus.

C. Electrons and protons are evenly distributed throughout the atom.

D. Electrons can be found anywhere within the atom without a fixed path.

During which type of radioactive decay is a positron emitted?

A. Alpha decay

B. Beta-minus decay

C. Beta-plus decay

D. Gamma decay

Which of the following has the greatest penetrating ability?

A. Alpha particles

B. Beta-minus particles

C. Gamma rays

D. Neutrons

The half-life of a radioactive substance is 8 years. How many years will it take for the activity of the substance to reduce to 1/8 of its original value?

A. 8 years

B. 16 years

C. 24 years

D. 32 years

Which of the following is NOT a beneficial use of radioactivity?

A. Powering spacecraft

B. Sterilising medical equipment

C. Enhancing plant growth

D. Treating cancer

a) Describe the Bohr model of the atom and highlight its main limitations. [3]

b) An electron in a hydrogen atom transitions from the n=3 energy level to the n=2 energy level. Calculate the energy of the emitted photon using the formula: E = 13.6(1/nf^2 - 1/ni^2) eV. [3]

a) Differentiate between alpha, beta-minus, and gamma decay in terms of their properties and penetration abilities. [4]

b) A radioactive sample emits beta-minus particles. What change occurs in the nucleus of the atom during this decay? [2]

a) Define the term 'half-life' in the context of radioactive decay. [2]

b) A radioactive substance has a half-life of 5 years. If you start with 100g of the substance, how much of it will remain undecayed after 15 years? [3]

a) Explain the concept of photon emission and absorption in relation to electron transitions in an atom. [3]

b) Using the formula E = 13.6(1/nf^2 - 1/ni^2) eV, calculate the energy difference when an electron transitions from the n=4 energy level to the n=2 energy level in a hydrogen atom. [3]

c) How does this energy difference relate to the energy of the emitted or absorbed photon? [2]

a) Describe the three types of radioactive decay: alpha, beta, and gamma. [3]

b) A certain radioactive element undergoes beta-plus decay. What changes occur in its nucleus? [3]

c) Why is it essential to use protective measures when working with radioactive materials? [2]