Physics

Fission reactions produce the most harmful radiation compared to fusion, chemical, or photo-chemical reactions. When a heavy nucleus undergoes fission, it splits into smaller nuclei and emits high-energy neutrons, gamma rays, and other ionizing particles. It also creates a variety of long-lived radioactive fission products that can cause significant biological damage and environmental contamination. Fusion reactions, while producing very high-energy radiation such as neutrons and gamma rays, generally produce fewer radioactive by-products and are considered to produce less harmful radiation overall. Chemical and photo-chemical reactions involve only electron rearrangements and do not emit ionizing radiation.

A capacitor (capacitance) blocks direct current (DC) because it does not allow a steady flow of charge through it, effectively acting as an open circuit for DC while allowing alternating current (AC) to pass.

Sounds with frequencies below 20 Hz are called infrasonic waves. This is because the human audible range starts from about 20 Hz, so frequencies below this are termed infrasonic.

The farad (F) is the SI unit of capacitance, which measures a capacitor's ability to store charge per unit voltage. Therefore, option C is correct.

The speed of sound in air depends primarily on temperature. At 20°C (room temperature), the speed of sound in air is approximately 343 m/s, which converts to about 1235 km/h (343 m/s × 3.6 = 1234.8 km/h). This is the commonly accepted average value under standard conditions. The formula to estimate speed of sound in air is c = 331.3 + 0.606 × T (in m/s), where T is temperature in °C. Multiplying by 3.6 converts m/s to km/h. Therefore, the correct answer is option C (1235 km/h). Option A (1347 km/h) is not a standard or typical value for speed of sound in air at normal conditions.

Nuclear sizes are typically expressed in fermis, which is a unit equivalent to 10^-15 meters, commonly used in nuclear physics to measure nuclear dimensions.

Side view mirrors of vehicles are convex mirrors because they provide a wider field of view, allowing drivers to see more area behind and to the side of the vehicle, which enhances safety.

The gravitational acceleration on Earth is approximately 9.80 m/s², which is the standard value used in physics for calculations involving Earth's gravity.

The visible spectrum of light ranges approximately from 3900 to 7600 angstroms (Å), which corresponds to wavelengths visible to the human eye. Options A and C fall outside this range, making B the correct choice.

Gamma rays consist of high-energy photons with very short wavelengths, making them the strongest photons among the options listed. X-rays also have strong photons but are generally less energetic than gamma rays. Microwaves have much lower photon energy, and 'Electromagnetic' is a broad category, not a specific radiation type.