Which if the following is a base
a) substance d contains carbon hydrogen oxygen and nitrogen
b) substance b gives off oh- ions that combine with h+ ions when dissolved in water
c) substance c is formed drom the reaction of an acid and base
d) substance a gives off h+ ions that combine with oh- ions when dissolved in water

B is the most probable answer.

A base is a substance that accepts hydrogen ions. When a base is dissolved in water, the balance between hydrogen ions and hydroxide ions shifts. The base "soaks up" hydrogen ions and the result is a solution with more hydroxide ions than hydrogen ions. This kind of solution is an alkaline solution.

Examples of bases include:

1. Potassium hydroxide

2. Ammonia

3. Acetone

5. Pyridine

6. Rubidium hydroxide

7. Sodium hydroxide

8.Zinc hydroxide

9. Methylamine

10. Lithium hydroxide.

the answer is a

photosynthesis