Which of the following instruments is used to measure air pressure?

a. Anemometer

b. Hygrometer

c. Barometer

d. Thermometer

C would be your answer as the root work baro means "relating to pressure"

Barometer is the instrument that is used to measure air pressure. The correct option among all the options given in the question is option "c". A barometer is a scientific instrument that is used in meteorology for measuring the pressure in the atmosphere. This instrument is made of a long glass tube that is open in one end and closed in the other. It contains mercury and is placed invertedly in a bigger container containing mercury.