At very high temperatures (around 1600 °C) incandescent metals glow white rather than red, so option D is appropriate.

Conversion of a photon into an electron-positron pair is known as pair production.

Twelve days is three half-lives (12/4 = 3), so remaining mass = 32 × (1/2)^3 = 4 mg.

Ultrasonic waves are mechanical (sound) waves requiring a medium, not electromagnetic radiation.

Option C is not a correct standard quark assignment (the notation shown is incorrect), so it is the incorrect assignment.

The Sun's energy is produced by nuclear fusion reactions in its core.

Emission of an alpha particle reduces the nucleon number by 4; beta and gamma emissions do not change nucleon number, so net change is -4.

A helium nucleus (α-particle) has charge +2e, equal to the charge of two protons.

In a cubic crystal, the lattice vectors are orthogonal, so the angles between sides are 90°.

By definition, one half-life is the time in which there is a 50% probability that a given nucleus will decay.