When using a manometer to check boyle's law, why is the pressure changed slowly? a. to avoid compressing the liquid b. to avoid compressing the gas c. to avoid changing the gas temperature d. to avoid changing the mass of the gas

Option C is correct.

c. to avoid changing the gas temperature

Manometers are devices using columns of a suitable liquid to measure the difference in pressure between two points and the atmosphere. A manometer is required for measuring substantial gauge pressures. It is the modified form of the piezometric tube.