Physics

Mach number is defined as the ratio of the speed of an object to the speed of sound in the surrounding medium. Therefore, it measures speed relative to the speed of sound.

Speed is a scalar quantity because it has only magnitude and no direction, unlike displacement, velocity, and acceleration which are vector quantities having both magnitude and direction.

Antimatter is composed of antiparticles corresponding to all types of particles, including anti-electrons (positrons), anti-protons, and anti-neutrons. Therefore, all the options listed are components of antimatter.

The resultant of two vectors with magnitudes 10N and 15N can range from the difference (15N - 10N = 5N) to the sum (15N + 10N = 25N). Therefore, 30N is not possible as a resultant magnitude.

A radian is a unit of angular measure, not length. Light year, angstrom, and micron are all units used to measure length or distance.

Velocity is defined as displacement per unit time. Displacement has the dimension of length (L), and time has the dimension (T). Therefore, the dimension of velocity is length divided by time, which is LT^-1.

Crookes glass is specially designed to cut or block ultraviolet (UV) rays, making it effective for filtering UV light. The other types of glass listed do not have this specific UV-blocking property.

The Coulomb force between two charges in a medium is reduced by the medium's relative permittivity (dielectric constant). For water at room temperature, the dielectric constant is approximately 78 to 80, meaning the Coulomb force is reduced to about 1/78 or 1/80 of its value in vacuum. This is a well-established physical fact. The option '1/78 times' (option C) correctly reflects this reduction factor. The option '1/58 times' (option D) is not accurate for water's dielectric constant at standard conditions. Therefore, the correct answer is C.

The resultant force of two forces can range from the difference to the sum of their magnitudes. For option C, forces of 3N and 6N can produce a resultant anywhere between 3N (6-3) and 9N (6+3), so 8N is possible. Other pairs cannot produce 8N as their maximum sums or minimum differences do not include 8N.

Vector addition obeys multiple algebraic laws: the commutative law (A + B = B + A), the associative law ((A + B) + C = A + (B + C)), and the distributive law with respect to scalar multiplication (k(A + B) = kA + kB). Therefore, the correct answer is 'All of these' since vector addition satisfies all these laws.