Which of the following equations represents a travelling wave?

Given below are two statements :

Statement I : PN junction diodes can be used to function as transistor, simply by connecting two diodes, back to back, which acts as the base terminal.

Statement II : In the study of transistor, the amplification factor $$\beta$$ indicates ratio of the collector current to the base current.

In the light of the above statements, choose the correct answer from the options given below.

Two electrons each are fixed at a distance '2d'. A third charge proton placed at the midpoint is displaced slightly by a distance x (x << d) perpendicular to the line joining the two fixed charges. Proton will execute simple harmonic motion having angular frequency : (m = mass of charged particle)

On the basis of kinetic theory of gases, the gas exerts pressure because its molecules :