Longitudinal waves cannot travel through:

Correct answer: (d) Vacuum

Explanation

Longitudinal waves, such as sound waves, are mechanical waves: the particles of the medium vibrate back and forth along the direction in which the wave travels. They need a material medium (solid, liquid or gas) to travel.

So they cannot travel through a vacuum. Electromagnetic waves, such as light, are different: they need no medium and travel through a vacuum.