Option 1: The statement is correct. The response of the ear to sound of increasing intensity is indeed approximately logarithmic. This means that as the intensity of a sound increases, the change in loudness perceived by the ear is not the same as the actual physical change in intensity.

Option 2: The statement is correct. The sensitivity of the human ear does not vary with the frequency of sound. This means that our ears perceive sounds of different frequencies with equal sensitivity, although there are certain frequency ranges where our hearing is more sensitive.

Option 3: The statement is incorrect. When two or more waves traverse the same medium, the displacement of any element of the medium is not necessarily the algebraic sum of the displacements due to each wave. Instead, it is the superposition of the individual wave displacements, which means that the waves combine to create a new waveform.

Option 4: The statement is correct. Longitudinal waves can indeed travel in all media, including solids, liquids, and gases. This is because longitudinal waves propagate through compressions and rarefactions of the medium`s particles, rather than requiring a specific type of medium to travel through.