Science

Matter

Matter is anything that has mass and take spaces, everything physical is made of mass.

Substance

Substance is a form of matter that has compounds, compositions, and distinct properties. For example like element.

Element

An element is a pure substance and it's made with only 1 atom 

Compounds

A compound is a pure sbustances made with more than 2 element.

Atom 

An atom is the smallest unit for an element that still retains the propeties of that element.

Molescule

A molecule is a group with more than 2 atoms bonded together.

 Air pressure affect boiling point , when  the air pressure is higher the boiling temperture is higher, when the air pressure is lower, the boiling point is lower.

At high places, like mountain, water boils below  100°C. Knowing this help people adjust cooking times and using some diffrent methods.
The pressure cooker trap the steam inside to raise the air pressure to cook the food faster and at higher temperature.

Knowing air pressure is useful at cooking and at science.

Use mass to identify new substance isn't good because mass isn't unique to a sphesific materials, and different substances can have the same mass like cheese burger and nutella. Also the mass only shows how much, it didn't shows what substance is it. I think the best property to use for identification is density, because  it doesn't change the amount of substnace, and it's unique to pure substances, and it can be measured or compare. Using the density help people to identify substances.