Which feature of a wave can be calculated using the formula below?

number of wavelengths / time

wavelength
speed
frequency
amplitude

The correct answer is Frequency.

Explanation:

Wavelength is defined as the distance between two crests or two troughs in a wave. Its unit is meters.

Speed of a wave is defined as product of its wavelength and frequency. Its unit is meters/second.

Frequency is defined as the number of oscillations happening in a given amount of time. Its S.I. unit is Hertz.

Amplitude is defined as the maximum displacement of a particle from its rest position.

Hence, the correct answer is Frequency.

water and alcohols have similar properties because water molecules contain hydroxyl groups that can form hydrogen bonds with other water molecules and with alcohol molecules, and likewise alcohol molecules can form hydrogen bonds with other alcohol molecules as well as with water.