Superposition affects amplitude but not the propagation speed, so the resultant wave's velocity remains unchanged.

The speed of light in vacuum is a constant and does not depend on frequency, wavelength, or amplitude.

Free oscillations of a mass-spring system require elasticity, inertia and a restoring force; gravity is not essential (it can be ignored or balanced).

de Broglie proposed that particles have wave-like properties (matter waves), formulating the relation λ = h/p.

Vibrations per second, cycles per second, and hertz all represent the same unit of frequency.

The phase angle specifies both displacement and direction in SHM; hence it is called the phase.

A sodium lamp emits light of a narrow wavelength (yellow) and thus approximates monochromatic light.

For 5 segments L = 5(λ/2) so λ = 1.0 m; adjacent antinodes are λ/2 = 0.5 m so first to third antinode is two intervals = λ = 1.0 m (100 cm).

A source moving faster than sound produces a Mach cone, so the wavefronts form a conical shape.

Waves that require a material medium and propagate via particle oscillations are mechanical waves, so option A is correct.