Question

Q. What remains the same before and after a chemical reaction?

1- the state of the substances

2- the number of atoms

3- the arrangement of molecules

Q. How many hydrogen atoms are in this chemical compound? C4H10

1- 14

2- 4

3- 10

Q. The connection between the atoms of a molecule is called a _____.

1- chemical reaction

2- chemical bond

3- chemical formula

Q. If 15 atoms take part in a chemical reaction, how many atoms will there be in the products?

1- less than 15

2- exactly 15

3- more than 15

Q.
In a chemical reaction, the rearrangement of atoms is started by the

1- breakdown of the bonds.

2- formation of the products.

3- breakdown of the atoms.


Q. Define chemical change and physical change?​

Answer 1

Answer:

In a chemical reaction the total mass of all the substances taking part in the reaction remains the same. Also, the number of atoms in a reaction remains the same. Mass cannot be created or destroyed in a chemical reaction.

10 hydrogen atoms

A covalent bond, also called a molecular bond, is a chemical bond that involves the sharing of electron pairs between atoms