Question

only after the discovery of ______ in the 1890s, could scientists begin to understand the true nature of chemical bonds. protons electrons oxygen neutrons rewatch

Explanation:

The discovery of electrons in the 1890s was crucial. Electrons play a key role in chemical bonding. Protons were discovered later (early 20th century), oxygen was known long before the 1890s (discovered in the 18th century), and neutrons were discovered in 1932.

Answer:

electrons