Thompson assumed that the amount of positive charge and negative charge in an atom was equal. Was this a reasonable assumption?

I really do not understand this.

The assumption made by Thompson, known as the "plum pudding" model, was based on the understanding of atomic structure at the time. According to this model, the atom was believed to consist of a positively charged "pudding" with negatively charged electrons embedded in it like "plums."

Thompson assumed that the positive charge and negative charge in an atom were equal because he observed that atoms overall are neutral, meaning they have no net charge. Since electrons were discovered to have a negative charge, he assumed that there must be an equal amount of positive charge to balance it out.

However, Thompson's assumption turned out to be incorrect. Subsequent experiments and advances in atomic theory, especially through Ernest Rutherford's gold foil experiment, revealed that the positive charge in an atom is concentrated in a small, dense nucleus at its center, while the negatively charged electrons orbit around it. The nucleus contains protons, which have a positive charge, and neutrons, which have no charge. The number of protons in the nucleus determines the element and determines the positive charge of the atom.

So while Thompson's assumption was reasonable at the time with the knowledge available, later experiments and theories provided a more accurate understanding of atomic structure by discovering the true distribution of positive and negative charges.