It's because of Avagadro's number.
- It is known as Avagadro's constant too.
- It states that at constant temperature one mole of any substance contain same number of atoms i.e n no of atoms
where

1. a) Igneous.
2. c) Metamorphic.
3. b) It broke into sediment and then compacted.
4. d) All types of rocks.
5. a) Wind and rain break down the rock into small pieces.
6. a) Yes, but it should be subtuced first.
7. c) Earth's interior.
8. c) Water.
9. b) Magma is molten rock within the Earth; lava is molten rock on the Earth's surface.
The mass will stay the same because of the conservation of mass
Answer:
they must have same atomic number and different atomic mass