жидкость

In a sentence

• Эта бутылка заполнена прозрачной жидкостью.

  This bottle is filled with transparent liquid.

  In this sentence, "жидкостью" is used in instrumental case to describe the contents of the bottle

• Нужно проверить уровень жидкости в двигателе.

  We need to check the fluid level in the engine.

  Here, "жидкости" is in the genitive case, indicating liquid as a measurable quantity within the engine compartment.

• Пожалуйста, не проливайте жидкость на пол.

  Please, do not spill the liquid onto the floor.

  In this usage, "жидкость" is used in accusative case, referring to liquid as an object affected by the action of spilling.