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.
Rules for estimating stability of resonance structures. 1  The greater the number of covalent bonds, the greater the stability since more atoms will have complete octets. 2  The structure with the least number of formal charges is more stable. 3  The structure with the least separation of formal charge is more stable.