Only after the discovery of __ in the 1890's could scientists begin to understand the true nature of chemical bonds. neutrons oxygen electrons protons

The correct answer is electrons.<br /><br />In the 1890s, the discovery of electrons allowed scientists to begin to understand the true nature of chemical bonds. Electrons are the negatively charged subatomic particles that orbit the nucleus of an atom and play a crucial role in the formation of chemical bonds between atoms.<br /><br />The discovery of electrons was a significant milestone in the development of modern chemistry and the understanding of the atomic structure. Prior to this, the nature of chemical bonds was not fully understood, as the existence of electrons had not yet been established.<br /><br />The other options provided are not correct:<br /><br />- Neutrons were discovered in 1932, not in the 1890s.<br />- Oxygen was discovered as a separate element in the 18th century, long before the 1890s.<br />- Protons were discovered in 1919, also not in the 1890s.<br /><br />Therefore, the correct answer is that the discovery of electrons in the 1890s allowed scientists to begin to understand the true nature of chemical bonds.