Circle the less dense item wood or water steel or water helium or air oil or water

1) Wood

2) Water

3) Helium

4) Oil

Explanation:

In order to compare the densities in each pairt, let's have a look at the values of the density for each substance/material.

1) Wood vs water

Density of wood is variable, between and depending on the type of wood, while density of water is : therefore, wood is less dense than water.

2) Steel vs water

Density of steel is around , while that of water is , so water is less dense than steel

3) Helium or air

Helium density is (at standard temperature and pressure) around , while the air density is about , so helium is less dense than water.

4) Oil or water

Oil density is around , while water is , so oil is less dense than water.

We can also use another method to compare the densities, without knowing their exact value. In fact, a substance 1 which is less dense than a substance 2 will float in substance 2, otherwise it will sink.

From common experience, we know that:

- Wood floats in water, so wood is less dense than water

- Steel sinks in water, so water is less dense than steel

- Helium floats in air (a helium balloon goes up), so helium is less dense than water

- Oil floats in water, so oil is less dense than water

answer: electrons