Question 01:

Matter is everything around us that takes up space and has weight. Things like water, air, and rocks are all matter. A substance is a kind of matter that is always the same, like pure water or salt. An element has only one kind of atom, like oxygen or gold. A compound is made when two or more elements join together, like water (H₂O), which has hydrogen and oxygen. An atom is the smallest part of an element. When atoms join, they make a molecule. For example, a water molecule has two hydrogen atoms and one oxygen atom. So, matter is everything, and atoms and molecules are the tiny parts that make it up.

Question 02:

Air pressure changes how hot water needs to be to boil. When air pressure is low, like on a mountain, water boils faster but at a lower temperature, so food takes longer to cook. When air pressure is high, water boils at a higher temperature. A pressure cooker keeps the steam inside, which makes more pressure. That makes water hotter and helps food cook faster and softer.

Question 03:

We can’t use mass to know what a substance is because many things can have the same mass. Mass only tells us how heavy something is. A better way is to use density, which means how heavy something is for its size. For example, gold is much heavier than wood, even if they are the same size. Each substance has its own density, so it’s easier to tell what it is that way.