The answer would be C) it is always the same as it was before the collision
Dalton's atomic theory was the first complete attempt to describe all matter in terms of atoms and their properties.
Dalton based his theory on the law of conservation of mass and the law of constant composition.
The first part of his theory states that all matter is made of atoms, which are indivisible.
The second part of the theory says all atoms of a given element are identical in mass and properties.
The third part says compounds are combinations of two or more different types of atoms.
The fourth part of the theory states that a chemical reaction is a rearrangement of atoms.
Parts of the theory had to be modified based on the discovery of subatomic particles and isotopes.
The correct option is B AND C.
An isotope is defined as two or more forms of the same element which contain equal number of protons but different number of neutrons in their nuclei, hence they differ in relative atomic mass but not in chemical properties.
Thus, isotopes has the same number of protons but differ in number of neutrons. Due to this fact, isotopes always have the same atomic number but different mass number. You will notice that the atomic number given for elements B and C are the same [101].
