When a thing does not give out any smell, we say it is odourless.

For example:

Air is odourless, but garbage has a stinking odour.

An oven is a small space or a chamber that is able to keep the heat inside. Due to this, the temperature inside the chamber is very high. The source of heat can be electricity, gas, firewood. Ovens are used not only for baking and cooking but a  potter also puts his clay pots into a "bhatti"  so that the pots gets fired at a high temperature. 

All types of breads (pav, sliced bread) are made in an oven. 

Defeated or solved a difficulty.

For Example: Gayatri overcame her fear of water after learning to swim.

Oxygen is a gas present in our atmosphere.

All living organisms need it for breathing and staying alive.

It is represented as O or O₂.

For example:

When leaves carry out photosynthesis, they give out oxygen.