An unknown substance was put in a container. the substance filled up the container from the bottom up, taking half of the space in the container. what is most likely the state of matter of the substance?

The state of the substance is most likely to be is liquid state.

Explanation:

States of matter of three types:

1) Solids: In this state of matter particles are strongly associated due to high inter molecular forces acting between them. They have a fixed shape that is they doesn't take the shape of the container in which they are kept.

2) Liquids: In this state of matter particles are associated due to weak inter molecular forces acting between them. They don't have a fixed shape that is they take the shape of the container in which they are kept. They do not occupy the whole volume of the container.

3) Gases: In this state of matter particles are very weakly associated . They don't have a fixed shape that is they take the shape of the container in which they are kept. They occupy the whole volume of the container.

The state of the matter most likely is liquid state.