Important Questions Test: Physical & Chemical Changes - Class 7 MCQ

Air and salt are not miscible and will not mix. Therefore no chemical reaction takes place.

A physical change is when a substance changes in ways like shape, size, or color but remains the same substance. It can often be reversed, meaning you can change it back to how it was before.

• When you cut a piece of paper into smaller pieces and then try to reassemble them, it is an example of a physical change, not a chemical change.
• Physical changes are changes that do not alter the substance's identity.
• In this case, cutting and reassembling paper does not change the paper into a different substance.
• It is just changing the shape and size of the paper.

When magnesium reacts with oxygen, it forms magnesium oxide. This reaction creates a new substance called magnesium oxide by combining magnesium with oxygen.

When you mix vinegar with baking soda, it creates a fizzy sound and you see bubbles coming out. This is because they react together and make something new. It's like a fun science experiment you can try at home!

• When carbon dioxide is passed through lime water, calcium carbonate is formed. This makes the lime water look milky.
• It's like when you mix milk and water together, they create a milky liquid.
• In this case, mixing carbon dioxide with lime water creates a milky substance called calcium carbonate.

• When something burns, it usually means it's changing into something new. This change is called a chemical change.
• For example, when you burn a piece of paper, it turns into ash. This transformation from paper to ash is a chemical change because a new substance is formed.
• So, the statement is TRUE.

The chemical name of baking soda is sodium hydrogen carbonate (NaHCO₃). It is commonly used in baking and cooking as a leavening agent and also known as sodium bicarbonate.