The most commonly used diagnostic tool for tuberculosis is a simple skin test, though blood tests are becoming more commonplace. A small amount of a substance called PPD tuberculin is injected just below the skin of your inside forearm. You should feel only a slight needle prick.
The structure has a double bond and an adjacent atom with a lone pair, so it could have resonance. The possible resonance structures are below. The first structure has the most common bonding pattern for all of its atoms, so it is a reasonable Lewis structure.
When more than one Lewis structure can be drawn, the molecule or ion is said to have resonance. The individual Lewis structures are termed contributing resonance structures. Resonance is a common feature of many molecules and ions of interest in organic chemistry.