Before coming into conclusion first we have to understand the nature of longitudinal wave and transverse wave.
The longitudinal wave is a type of mechanical wave in which the direction of wave propagation is parallel to the particle vibration.In such type of wave one will notice compressions and rarefactions.
Compressions are the high pressure zones where the particles are very close to each other and rarefactions are the low pressure regions where there is large separation between particles. Hence a longitudinal wave is a series of compresions and rarefactions.
The wavelength of a longitudinal wave is the distance between two successive compressions or rarefactions. Hence the wavelength is measured parallel to the direction of wave. As the particle vibration is parallel to wave propagation ,so the amplitude of the wave is measured parallel to wave direction.
Transverse wave is such type of mechanical wave in which the particle vibration is perpendicular to wave propagation.Here crests and troughs are formed.
The distance between two successive crests or troughs are called wavelength which is measured parallel to the wave propagation. As the particle vibration is perpendicular to wave propagation,so the amplitude of the wave is measured perpendicular to the wave propagation.It is so because amplitude of the wave is the maximum distance travelled by the particle from equilibrium position.
Out of the four options given in the question only the option 3 is correct .Other options are wrong as violate the nature of longitudinal and transverse waves.
