Physics

Gamma rays (γ-rays) have the greatest penetration power among the listed radiation types because they are high-energy electromagnetic waves that can penetrate most materials more deeply than alpha, beta, or neutron radiation under typical conditions.

Pair production cannot occur in a vacuum because momentum cannot be conserved without a third body to take up recoil momentum. Energy, charge, and mass conservation are not violated, but momentum conservation requires interaction with a nucleus or another particle.

Radioactive decay follows an exponential decay law, expressed as N = N₀e^(-λt), where N is the quantity remaining, N₀ is the initial quantity, λ is the decay constant, and t is time. This formula correctly represents the decrease in quantity over time.

Lead is a dense material with a high atomic number, making it very effective at absorbing and shielding against gamma rays compared to lighter materials like water or aluminum.

Physical quantities are generally divided into two main categories: fundamental (or base) quantities and derived quantities. This classification helps in understanding and measuring physical phenomena.

Uranium has several isotopes with different numbers of neutrons. For example, Uranium-235 has 143 neutrons, while Uranium-238 has 146 neutrons, so the number of neutrons varies depending on the isotope.

Gamma rays (γ-rays) have high penetrating power and are commonly used for sterilizing medical instruments and supplies by killing bacteria and other pathogens. Alpha and beta rays have less penetration and are not suitable for sterilization. Option D is incorrect as beta rays do not have equal antiseptic properties compared to gamma rays.

An ideal standard of measurement for a base quantity should be accessible, meaning it can be used or realized easily, and invariable, meaning it does not change over time. Therefore, both 'Accessible' and 'Invariable' are correct characteristics, making option D the correct choice.

Carbon-14 (C-14) is widely used as a tracer in biological and environmental studies due to its ability to integrate into organic molecules, making it very useful for tracing biochemical pathways and dating. The other isotopes listed have more specialized uses but are less broadly applicable as tracers.

Significant figures in a measurement include all the digits that are known accurately plus the first doubtful (or estimated) digit, which reflects the precision of the measurement.