Conduction, wave motion, and radiation are all mechanisms by which energy can be transferred, so 'All of these' is correct.

For a fluid with fixed bulk modulus, wave speed is inversely proportional to the square root of density, v ∝ 1/√ρ.

Frequency f = 1/T = 1/1.42 ≈ 0.704 Hz, approximately 0.7 Hz.

For x = A sin φ, displacement is maximum at φ = 90° (sin φ = 1).

Wave speed on a string v ∝ 1/√(mass per unit length); if mass per unit length increases 4×, speed becomes 1/2 of original.

The restriction to a discrete set of allowed frequencies in stationary waves is described as quantization of frequencies.

Polarization typically reduces the net intensity (e.g., ideal polarizer transmits half the intensity of unpolarized light), so polarized light is less intense.

Each third has constant 3k; three such springs in parallel give total k_total = 3·(3k) = 9k.

In longitudinal waves the particle motion is parallel to the direction of wave propagation, so they fit the description.

Amplitude refers to the maximum displacement from the mean position in oscillatory motion.