Final answer:
The structure of an atom is described by a negatively charged electron cloud surrounding a positively charged nucleus.
Step-by-step explanation:
The correct phrase that describes the structure of an atom is: B. a negatively charged electron cloud surrounding a positively charged nucleus. The nucleus at the center of the atom is positively charged, consisting of protons with a positive electric charge and neutrons with no charge. Electrons, which have a negative charge, are distributed around the nucleus in a region that is commonly referred to as an electron cloud. This cloud carries a net negative charge. In an electrically neutral atom, there are as many electrons in the electron cloud as there are protons in the nucleus, balancing out the overall charge of the atom.