Final answer:
The statement that the electron theory of matter assumes atoms contain negative and positive electrical charges is true. Atoms have negatively charged electrons and a nucleus with positively charged protons, balanced to make atoms electrically neutral.
Step-by-step explanation:
The electron theory of matter assumes that atoms are composed of negative and positive electrical charges. This is true. Atoms consist of negatively charged electrons, which were first identified in cathode-ray-tube experiments, and a positively charged nucleus.
The nucleus contains positively charged protons, which along with electrons, contribute to nearly all observable charge in nature. Neutrons, the third component, are neutral and carry no charge. Atoms are electrically neutral because they contain equal amounts of positive and negative charge.
Thomson's model proposed a plum pudding structure with electrons embedded in a positive sphere, but Rutherford's later experiments revealed the existence of a dense, positive nucleus, fundamentally altering the understanding of atomic structure.