Allochemic juglone is produced by
A. Walnut
B. Sunflower
C. Barley
D. Eucalyptus

Hint:Juglone is an allelopathic organic compound. Juglone is a toxic isomer of law stone which is the pigment that stains henna leaves. In the food industry, it is also known as Natural Brown 7. It has other names such as nucin and regianin. It bears the chemical name- 5-hydroxy 1,4- naphthalenedione (IUPAC). It acts as a growth stunner mainly among other toxic effects.

Complete answer:
- Juglone is naturally present in almost all parts of walnut trees, especially in nuts, roots, buds, and hulls.
- It is mainly present in the black walnut (Juglans nigra).
- Juglone's toxic property inhibits the growth of nearby sensitive plants.
- It mainly affects the growth of vegetables such as tomatoes, potatoes, the pepper plant, and the eggplant.
- It leads to stunting, wilting, yellowing, or even death of the plant. It has the worst effects on the crown of the tree.
- Juglone has no ill effects on humans. If dogs chew the leaves accidentally, they may be affected by Black walnut toxicity.
- It is completely harmless to the cats.
- Juglone doesn’t spread far because it is not soluble in water. Its range is within 50-60 feet from the trunk.
- It acts by inhibiting certain enzymes required for metabolic functions thus inhibiting vital processes like photosynthesis and mitochondrial respiration.

So, the correct answer is option A.

Note:
 A toxin like juglone can't easily be neutralized. Juglone naturally degrades itself within the time period of 2-4 weeks. It remains in the soil for longer periods (two months after the tree has been cut).