The correct option is **D. Gamma rays**. ### Detailed Explanation 1. **Understanding Electromagnetic Waves**: Electromagnetic (EM) waves are a form of energy that travels through space. They are characterized by their wavelength (λ) and frequency (f). The frequency of an EM wave is the number of cycles that pass a point in one second, measured in hertz (Hz). The relationship between frequency and wavelength is given by the equation: \[ c = f \cdot \lambda \] where \(c\) is the speed of light in a vacuum (approximately \(3 \times 10^8\) m/s). 2. **Energy of Photons**: The energy (E) of a photon is directly proportional to its frequency and can be calculated using the formula: \[ E = h \cdot f \] where \(h\) is Planck's constant (\(6.626 \times 10^{-34}\) J·s). This means that as the frequency increases, the energy of the photon also increases. 3. **Frequency and Energy of Different EM Waves**: - **Radio Waves**: These have the longest wavelengths (ranging from about 1 mm to 100 km) and the lowest frequencies (from about \(10^3\) Hz to \(10^{11}\) Hz). Consequently, they have the lowest energy per photon. - **Microwaves**: These have shorter wavelengths than radio waves (ranging from about 1 mm to 1 m) and higher frequencies (from about \(10^{11}\) Hz to \(10^{14}\) Hz). Their energy is higher than that of radio waves but still relatively low. - **Infrared Radiation**: This type of radiation has wavelengths ranging from about 700 nm to 1 mm and frequencies from about \(10^{14}\) Hz to \(10^{15}\) Hz. The energy per photon is higher than that of microwaves and radio waves. - **Gamma Rays**: These have the shortest wavelengths (less than 0.01 nm) and the highest frequencies (greater than \(10^{19}\) Hz). As a result, they possess the highest energy per photon among all types of electromagnetic radiation. 4. **Conclusion**: Since gamma rays have the highest frequency, they also have the greatest energy per photon. This is why option D is the correct answer. ### Why Other Options Are Incorrect: - **A. Radio Waves**: They have the lowest frequency and energy, making them the weakest in terms of photon energy. - **B. Microwaves**: While they have higher energy than radio waves, they are still significantly lower than infrared radiation and gamma rays. - **C. Infrared Radiation**: Infrared has more energy than radio and microwaves but is still less than that of gamma rays. ### Common Pitfalls: - Confusing wavelength with frequency: Remember that shorter wavelengths correspond to higher frequencies and vice versa. - Misunderstanding energy relationships: Always use the formulas \(E = h \cdot f\) and \(c = f \cdot \lambda\) to clarify energy and frequency relationships. ### Revision Summary: - Gamma rays have the highest frequency and energy per photon among electromagnetic waves. - Energy of a photon is directly proportional to its frequency. - Radio waves have the lowest energy, followed by microwaves, then infrared radiation, and finally gamma rays with the highest energy. - Remember the relationships between wavelength, frequency, and energy to avoid common mistakes.